Kirin - having run windows 7 on three different machines, a couple of points:
1. Sound cards - I would recommend finding a decent sound card like a Sound Blaster X-Fi XtremeGamer. I found that using the onboard sound drivers caused a lot of headaches with stuttering when the game got busy (i.e. base in flames, planes attacking, warning siren going off, planes taking off, dogs and cats flying everywhere).

2. Hi-rez - I too had a lot of grief with the game freezing all because of a mis-installed hirez pack. You did the right thing re-installing it.
3. Chipset - although Windows 7 does a bang-up job finding most of your current drivers, be sure you have the latest chipset drivers.
Glad to hear it's working for you now.
