This can be a few things.
If this is an existing machine and you have had problems in the past, I would recommend that you use Memtest86+ and do a scan of your system just to make sure there is no faulty memory.
Next, or if you have had no issues in the past, Windows 7 is a leap forward, however, there are a few out of the box drivers which are pretty awful (even though they are signed). I have had a lot of problems with Realtek network drivers that basically cause a BSOD whenever (in the movie speed style) the network reaches above 70% utilization. You may be affected by this or another driver so I would recommend upgrading to the latest available versions.
Again, I can say 100% sure that Realtek drivers have problems and updates available here, I have not seen BSOD with other manufacturers but I have seen much increased performance by upgrading.
Lastly, if this doesn't help, I would recommend downloading Nirsoft Bluescreen View which can tell you what caused BSODs on your system. If you edit your question and post them, we can help you further.