a 220 watt PS. Since WiFi adapters consume more power than modems, I have to wonder if the power supply isn't marginal for the configuration.
I've tried 2 different PCIe wifi cards, first being aBit airPace and the second being an ASUS PCE-N13. Upon the install, both will work initially but after a while, they will cause the PC to randomly reboot. Currently running Win7 x64. PC in question is a Gateway SX2800. Also, the machine came with a 56k modem installed in the same slot which never caused a problem.