Help getting rid of viruses and spywares.

Hey I use this computer to do important business on this and really don't want any viruses or spywares on it because I use credit cards on this. So please help me! I have McAfee but this is really bad since it doesn't detect anything but I keep getting this message -

Attention, ! Some dangerous trojan horses detected in your system. Windows Vista (TM) Home Premium files corrupted. This may lead to the destruction of important files in C:\WINDOWS. Download protection software now!

Click OK to download the antispyware. (Recommended)

Please help me get rid of this and any other viruses/spywares.

 

Welcome to WindowsBBS helpneeder

If you're still in need of assistance, lease read this topic, install the latest version of Hijackthis, run a scan and save the log (you can close it for now). Then, download and run Deckard's System Scanner and post BOTH the main.txt and extra.txt logs. You may be required to put them in separate posts due to character count limitations.