If this is going to be a one man gig/small team effort I would instead suggest you make a heuristics module rather than a signature detection not least of all because signature detection has barely worked for about 10 years now and even if you did believe in it a good database is millions of entries large (most people making new ones will buy an old AV company/rights to a database and work from there).
Usual heuristic checks are directory access, monitor certain key directories and registry entries (especially startup and in event of* , scan for runtime compression (I find this is what often triggers false positives so be careful), network access (granted this is firewall territory), hooks that are added, many programs are still static so binary overwriting can be a useful flag, maybe also consider a sort of sandbox mode (a safe installer/uninstaller would be great) and while you are at all of this you will want to harden your tool against the malware itself (usually by using the same/similar techniques to the stuff you are trying to defeat).
For bonus points you might consider a malware cleaner (indeed 7zip often works for me here) to rid people who like keygens and similar little programs of the small 7 kilobyte loader type malware that they get wrapped in between the scene and the places us plebs find stuff.
*my most disliked malware at the moment are the false AV programs (XP Security Tool 2010, XP Defender Pro, and Vista Security Tool 2010 to name 3 of them) that change the way executables are run among other things.
Better yet you could go the opposite way and secure systems/provide a means to do it- windows 2K and XP SP2 have now ceased support and as such could do with a few tweaks in that direction (see some of the stuff people did to windows 98) similar to the things like XP tweaker but with a large focus on security.
"Or you can post the virus source here"
Such a thing is not so good (not least of all because it would be a skiddies wet dream)- the best you can really do here is a virus toolkit.
