Sorry I'm a little late to the party here but hopefully I can help out some.
Two key pieces of advice. One if you haven't chased much, go out with someone who has until you know how you will react when the going gets hairy. I've seen perfectly calm normal rational people practically lose it when things get hairy and trust me they will get hairy. Also it's very nice to have someone with experience with you because you can watch tv, movies, and see pics on the internet all you want but things are VERY different when you are right there under a super cell. It's also great to have a second person to have a second set of eyes on the storm. New rotation, or RFD can sneak up on you. I know that sounds stupid, but it can.
The second pieces of advice is about cameras. Get an SLR. Just do it, if you think this is something that's going to be a lifelong hobby for you make the investment. I tried to get by with a high end point a shoot for a while and the difference between a point and shoot (even a high end one) and an SLR is night and day. The quality of an SLR is just that much better, especially in low light performance, which is basically most thunderstorms.
Don't be afraid to buy used! Many photogs baby their gear which is great because it means there is a lot of quality on the used market. There are several sites like Adorama and B and H who have a nice selection of used gear.
I'm a Canon guy personally and shoot with a 60d. I love the d series because the controls are all separate, easy to access, and intuitive. Also the bodies feel substantial in your hands which makes them easier to work with and hold IMO. The rebel series is nice and a cheaper alternative but if you have big hands like I do they aren't that comfy.
Get a tripod. You can get something that is decent in the 60-100$ range. Also a circular polorizing filter is nice to have. Spend some money here and get a decent one. As for lenses, I go by the theory of getting one good versatile lens goes a very long way. Depending on what system you go with you will have different lenses to choose from. The great thing about SLRs is that you can build your system one piece at a time.
Lastly, practice practice practice. Digital photography is great because your mistakes aren't costly, but time is so before you head out chasing you need to know your camera like the back of your hand and how to change settings quickly. Also you need to be able to identify a scene and adjust your settings to it quickly. This only comes with experience in shooting.
Have fun and be safe!