first of all congratulations KK. a firefighter is a very rewarding job, my cousin seems to think so.
it depends what you have now. if you have say...a gf3, or a radeon8500, i would wait a while to make an investment on say, the nv30 or 9700, something that will take you to the limit and last longer.
although, i got a nice ti4200 for 143 dollars on
http://www.newegg.com
works like a dream. every game i have is nice and smooth, and this is coming from a 1 1/2 year old econoPC POS.
i would say the ti4200 is more of a temporary solution that will last until you can afford the bigger and better cards and newest chips from Nvidia or ATI, depending upon which you prefer