well your Virus Definations are stored in ..
c:\Documents and Settings\All Users\Application Data\Kaspersky Anti-Virus Personal\5.0\Bases
just copy paste all the files from bases folder ..and next time after reinstall..go to settings...configer updates...select update from Local Folder ..and all teh files will be Updated...
and remember the previous and new Av sud b of same version......updates of 1 ver are not compatable with other..u will get a Database Corrupt error