Look for a reptisun 5.0 or reptiglo 5.0. Florescent lighting does come in tubes, but there's another kind called compact florescent which are twisty shaped or sort of prong shaped that can screw into a regular light socket. Here's a pic of what you need:
http://www.zoomed.com//assets/images/FS-C510.jpg Petsmart and Petco usually carry them, if not you can order them online at
www.reptilesupply.com or
www.reptiledirect.com.
To try to answer your specific question, the wattage of the uvb bulb doesn't matter as much as the percentage of uvb output. You want about 5% for an RES. Reptisun 5.0 is great for that, but if you have to go with another brand make sure it says at least 5% uvb output. Where wattage matters is with your basking bulb. Its purpose is to provide heat, so depending on how far away your fixture is from your basking area, you need to determine what wattage will heat it to about 10 degrees higher than your water temperature. It might take a little bit of playing around to get it right. I think a lot of people use regular 60 watt lightbulbs, it doesn't need to be a special bulb.
Hope this helps!