(Disclaimer: I'm not an expert)
Minimum requirements can be found here:
http://wiki.guildwars.com/wiki/Hardware_requirements
GW, given its age, runs on pretty much anything nowadays. They (Arenanet) stated a while back that they weren't going to support Windows 95 anymore, so that should give you an indication of what I mean. Of note however, is that GW doesn't run natively on non-windows systems, so you need something that helps with that (again, see the above link).
In any case, a free trial is available
here. You can always try to get that running.
(Also, if you're referring to GW2, you're in the wrong place.
See here instead.)