joyea
If you were able to run the program in safe mode, and if you were able to get the updates and do an immunise, then the immunise entries remain until you remove (undo) them. Spybot doesn't need to be running for them to remain effective. Teatimer can obviously not be used in your situation. If you are using Internet Explorer, then as an add on to IE, SDHelper should also work (you would need to confirm this).
Whether being able to get the regular detection updates and carry out the associated reimmunisation is practical is another thing.
As your problem may be related to the amount of memory available, it might be worth you checking availability and cost to increase the memory to 512MB. Most local computer service companies would be able to give you that information, however to some extent it would be prolonging the inevitable and you should keep this in mind when looking at costs. (It's also possible that increasing the memory may not fix the problem). The other option of course is to simply run what you can on it, and do without the software that won't run.