AVG has had a few false positives lately. I just installed AVG free and had it do a scan of my OO2.4, and it hit on program/msi-pkgchk.exe.
I've checked the file with virustotal.com, and out of 36 anti-virus tools, only AVG flags it as a trojan. Is AVG right, and all the others wrong?
If you have AVG pro, you can contact support so they can verify that the file is safe and update their database. Once they do an update, you can move the file from the vault (if you've told AVG to quarantine it) and everything should be back to normal.
OOo 3.3.X on Ms Windows XP