Blade, thank you so much. I ran NAV, Spybot and Ad-Aware as usual (I run them all on a daily basis) and they all came up clean. I've also ensured that my Microsoft Updates are all set as always (which they are). I enabled Windows Firewall and downloaded the other three tools you mentioned.
Thank you again for helping me out - hope that this is the last of the infection! If anything changes, will let you know