Yes and no. Yes Windows 7 natively supports USB 2.0, but it may not necessarily support some random PCI card which happens to have USB ports on it.
Go to the website of the company that makes the PCI card and check for any downloadable drivers from them and/or troubleshooting steps. I've found a lot of times people will buy the cheaper "OEM" versions of products which don't come with the usual assortment of software found with the retail versions. People just look at the cheaper price and don't dig deep enough to figure out that you're only getting the hardware in an anti-static bag, nothing else.
Having run out of USB 2.0 ports, I installed a 4 port controller in a free PCI slot on ABIT IP35 Pro (LGA775) MB. OS is Win7 SP1 32-bit. Win7 doesn't recognize the card and flags it as an Unknown Device (Code 28: Drivers for this device are not installed). No software came with the USB controller. Also, doesn't Win7 natively support USB 2.0 devices. While this isn't my main system, it is my storage host.
Thanks for any tips to solve this issue.