[quote name='J7.']Can you buy stuff for PSP using the PS3 PSN cards sold in B&M?[/QUOTE]There are no PSN cards yet, but they are coming this year (in $20 increments).
That's kind of strange, because I know of a few retailers in my area who carry Wipeout Pure (I know Meijer, which you probably don't have, has it on clearance, I think). But if you can't, you can eventually download it (I already own a copy, so I won't).
If I was in your position, I'd just wait for Pulse. Custom soundtracks seem too awesome along with online play (I think it has it). Although I'm mostly interested in Wipeout HD right now (since I'm a PS3 owner), I'm still going to get Pulse.