Don't buy software from Ebay unless the user has a very high rating. It could be an illegal, pirated version that doesn't work... There's a list of obvious reasons. If you do, don't spend much.
Allways downloaded the demos of products before buying them, if you don't have broadband you can allways find demos on video magazines, such as http://www.digitmag.co.uk
Make sure the demo works on your pc, and if it doesn't... email the software company and ask about it.
Don't go with some cheapy budget programme. They're crap, if you want cheap... download the free Avid FREEDV (which is actually quite good)
EDIT : Just saw Otteypm posted the same link, didn't mean to copy I didn't realise...
Back to Photoshop (PS) v Photoshop Elements (PSE).
I have PS7 and PSE1, and I have to say... there isn't much PS7 can do that PSE1 can't.
Infact, I'd say PSE1 is MUCH easier to use. PSE2 can do even more, but definitely consider buying Photoshop Elements if you can't afford Photoshop.
Don't be a sheep either, Premiere certaintly isn't the best video editor around. For some people, it's 'the best' but I prefur Vegas Video and Ulead Media Studio Pro.