Hmm reformat seems rather extreame.
I personally recommend your use a trial of kaspersky 6 along with Ewido to clear out your viruses/malware and then use Avast ongoing (unless you want to buy kaspersky).
Might be worth running some rootkit scanners e.g. blacklight or rootkitrevealer
A trojan may well hide in your system restore points so clear those too.
Intel core I7 920
6GB OCZ platinum 1600
Samsung 1TB F1 Spinpoint
Samsung SM2443BW 24"