I'm using msysGit on windows7 in a 32bit environment. I'm really new to git so I don't know what else I would need to explain here to help. One thing I can tell you is this repo is a git clone from my svn repo
Looks like you are experiencing the same issue as: Repack of Git repository fails
They suggest running:
git config pack.windowMemory 10m
git config pack.packSizeLimit 20m