Open up the case, look for the motherboard model printed on the board itself and then use that to point to manufacturer and download appropriate XP drivers. Vista or W7 would be too much for this machine.
The worst part about the lack of support is that with 4GB or ram the system would run everything just fine despite the comments above
I wouldn't necessairly agree with this but sometimes you can get your older machine running windows 7.
Although it is a hunt and sometimes you have to manually install / configure things, it is possible to get drivers for older hardware. Especially when people start to understand that most Vista drivers will work under Windows 7.
A 1.6ghz Pentium 4 is getting a bit long in the tooth. It would struggle with all but the most basic applications even with 4GB of ram. If you are very patient and understand that at best it would be an "office" machine then yes, the hardware is still somewhat viable.