You need to tell us what you've got, then we'll tell you what you need.
I ran into a similar problem. I had an Athlon 1.2GHz processor with a 64MB video card in my machine, and Bloodlines would install, launch and start running up until I wanted to start the character creation process, at which point it would stop and I needed to Alt-Tab out and abort the program. I took my machine to my local computer store and they sold me a Radeon 9600 video board (256MB) and dropped a new 1.6GHz processor in the motherboard and sent me home again. Now Bloodlines plays just fine .. there are some performance issues still, but the game is very playable and the issues tend to clear up as more of the game loads into memory. I have 512MB of RAM.
Hopefully in the near future I plan to take my PC back to the store and max out the RAM and processor capability, but I expect that will cost me some money I don't have at the moment. Once I get that done, though, I can't wait to play Bloodlines, cause it will rock.
Edit: By the way, the system requirements indicate that you need a 1.2GHz processor (or better), 384MB of RAM (or more), and a video board that can handle DirectX v9.0. I think the video board was the missing link in my configuration .. you need to make sure you have these minimums before playing the game. I'd strongly recommend more than the minimums, however, especially RAM and video RAM, as this is a very graphics-intensive game.