An Ubuntu Linux question

Question for the Linux people in the audience: I have a PC at home (don’t know the exact hardware stats offhand) that’s running WinXP. The machine is old and I have no idea where the install disc for WinXP is. And WinXP is driving me crazy on this machine for a number of reasons, so I’d like to think about switching it to Linux, specifically Ubuntu because it seems well-supported and I’ve had good experiences with Ubuntu. However, if I install Ubuntu and it doesn’t play nice with my PC, I don’t know where the WinXP install disc is and so I won’t be able to go back. And I’d rather not have to set up a dual-boot system; I know how to do that and manage the system, but the PC is for my kids and I want to keep it simple. 

So, is there a way to try out Ubuntu, just to make sure core hardware stuff like wifi works, without wiping stuff out and installing? 

UPDATE: The partitioning tools virusdoc was mentioning are: 

http://qtparted.sourceforge.net/features.en.html
http://en.wikipedia.org/wiki/Ntfsresize

These were getting caught in the spam filter.