It may be the software added but doubtfull, both of those have been tested with winxp. Any hardware added recently? You say you have patched for the recent worm, did you have all the prerequisites for xp for the patch (i think it wanted the latest service pack.). Antother posibility is virtual memory,, is your HD almost full? A final option may be a bad pice of hardware, is the HD makeing noise, run a scan disk run a ram tester on your ram.