Most people who have upgraded their OS don't realize that windows.old even exists on their machine.
In a manner of thinking, windows.old is similar to a "parallel installation of Windows" and includes not just the prior Windows OS, but all the applications previously installed, all the Users, and all the data belonging to those users.
They never notice it, and probably wouldn't know what to do with it if they ever did need it.
Just as a FYI...Here's the MS instructions for restoring from windows.old (again, this is just FYI and I am not suggesting that you use it at this time, and probably never)
http://support.microsoft.com/kb/933168
Yes, windows.old is "clutter", and can be removed...... ****BUT
If ever this OP needed to restore the machine to the prior OS, at that time windows.old would be "essential".
Whether or not it becomes an important issue to this OP depends upon any future occurance of catastrophic failure and more importantly depends upon what other backup/restore options they have available.
e.g. Does OP have available in their possession:
OEM factory restore CD (related to the prior Windows installation)
Installation media for this current Vista Basic
.iso full drive and partitions backup (i.e. Acronis or Macrium, or similar)
*This machine probably does not have a system recovery partition, the likes of which come standard on OEM computers with pre-installed Windows where there is no accompanying CD/DVD installation media.
**I say this because OP describes throwing this machine together in collaboration with other high schoold buddies, therefore they would probably not have been Microsoft Partners, and would not have used Microsoft OPK (OEM Preinstallation Kit) through which they might have included the creation of a recovery partition on the machine Hard Drive.
Arguement against "using" windows.old:
Using windows.old would result in the machine reverting to XP or whatever prior OS had been installed.
Note: There is different situation in which windows.old "might" be essential...
That is, (If the installation of Vista Basic was an "upgrade")
In that case, if ever the OP needs to reinstall Vista Basic as an Upgrade, they will also be required to provide "proof of prior qualifying OS" to support the upgrade.
Reinstalling Vista Basic (as an upgrade procedure) would benefit from the existance of Windows.old as the qualifying reference.
Therefore, my recommendation:
>> Keep Windows.old. <<
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Other considerations:
OP has 102.66 Gb Free Space on C:\ which is about 22% of their 500GB HD.
That should be sufficient (at least for now)
And any gain from deleting windows.old would be trivial.
Other observations:
We don't know if windows.old is "competent".
IF it is not, then it is wasted space.
IF it is, then it "might" be needed and useful in the future.
and I don't know any method for verifying windows.old, except to actually use it to try to restore to prior Windows OS and configuration.
(** I am "not" suggesting to do that, since OP apparently wants to continue with the current Vista Basic and you don't want to throw OP back to whatever they had before Vista Basic)
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Unrelated Observation:
OP initially had 149GB Free Space on C:\
--- then you instructed some procedures
After which OP had 102GB Free Space on C:\
What's up with that?
Do you anticipate that when you do your final cleanup and uninstall the various speicialized tools, that the Free Space will then be recovered?
Further Unrelated Observaton:
This machine has several Game installations plus Steam installation to make the games run(better).
There are also game related utilities such as Ventrilo and download assists and bearshare
There seem to be a bunch of broken Registry Items.
Even the Registry Reference to Paging File seems to be missing or broken.
You have rightly cautioned OP to avoid using automated Registry Cleaners.
But the damage may already have been done.
If ever there was a machine, OS, configuration, and installed applications that was ripe for a Format and Reinstall... this might be it.
On the otherhand, the machine is running.
It would be tedious, time-consuming and possibly costly to go through the process of downloading and reinstalling all of those games and utilities after formating and reinstalling and updating Windows Vista Basic.
Depending upon OP's intentions (Maybe OP will be using the machine only for school work, office functions, and browsing)...
If OP wishes to continue with the same gaming activity, they might be better off just continuing as is.
But if they are moving away from gaming, a fresh installation may improve the function and avoid residual conflicts.
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I don't know how to repair the Registry link for Paging File.
But Paging / Swap File pseudo-ram resources might improve gaming functionality.
What I would do....
Go to Start - Computer - (right-click)Properties - Advanced(tab) - Settings(button)
I would select:
"No Paging file"
apply
OK
Reboot.
Go to Start - Computer - (right-click)Properties - Advanced(tab) - Settings(button)
Then Select: "Automatically manage paging file size for all drives"
Apply
OK
Reboot
Paging File "should" then be addressed and available without errors in the Registry links.