filesharing between computers on a wifi router

[TigerUK]

I've got a basic wifi router only for internet connection set up right now,

I often share files between my laptop and desktop with the use of a USB thumb drive, but it's a bit of a hassle having to plug in a thumb drive, transfer files and then reinsert the thub drive onto the other machine.

Is there a quick way to do this via the fast wifi network (rather than emailing large amounts of data).

 

[TigerUK]

both are XP, however I will be upgrading one to windows 7 soon.

I wouldn't mind buying a adsl router with a built in hard drive which can be used by all the comps on the network as a storage device, if that is an option.