my switch in one of my doors is broke so that when i have my dome light bulb in it never turns off. does anyone know how or how hard it is to replace?

Dead easy. Same thing happened to me on my 2004 4door cav. Get a brand new switch from GM - a 2nd hand one might not work as they self-adjust themselves to your particular car the first time you close the door. Pull the old one straight out with a pair of pliers (the retaining clips will break meaning you won't be able to put it back in very well, so be sure it really is the broken switch!) disconnect the wiring plug and simply connect and push back in the new switch!

HTH

where can i purchase one?

Just explain what you need to your friendly local chevy dealer's parts desk :-)

If you don't have one nearby, I'm sure any GM dealer can supply a matching part.

10 second fix- .....8.50 retail and tx. 10.00 fix at worst.