Rather then dual booting or live CDing I would recommend a 3rd path..
I used to run Xandros v2.0 Pro Linux on a dual booting PC in 2004 with WindowsXP, and after a few months of virus free bliss WindowsXP decided to die all of a suddern, and took the Linux with it (like a drowning man pulling under his would-be helper).
Because of this a lot of my office work done on Linux died with the machine (95% of was backed up though).
Recently I have gone back to linux, and this time I went onto eBay and bought myself the barebone parts to put together an old system that would run fine (Pentium3 1ghz, 256mb ram, 20gb HDD) cost me around £47 or something ($65 US?) and gave me a working PC that could handle most of the Linuxes out there..
Went through a few Distos of Linux until I settled, and as a Linux "Newbie" I just wanted something I could surf with (using Firefox) and do office work (using Openoffice) while my main PC would run XP and be used for nothing bu playing games..
I tried, Fedora (average), SimplyMepis (good but made for newer PC's), DSL (fast but too basic), Mandriva (good but again, need a better PC), Ubuntu (impressive) and Finally Xubuntu (fast as well!).
I'm still using the Alpha version of Xubuntu (which is released in June), but its rock solid, fast as hell on a 1ghz PC (equal to my 3ghz Intel630 machine while surfing), and the only thing it lacks is proper networking tools.. which will hopefully be in the final release..
So thats my opinion, Linux DOES take time to learn and get a handle on, but you don't need a ninja PC to run it, so build or buy a piece of crap from eBay and you can take your time and play around with Linux without any fear of altering or modifying your gaming PC.