Purchase help: New MBP uni vs. older used MBP

Exclusive PC user who has been contemplating switching to Mac for sometime. Have only used a Mac a handful of times and usually only to browse the web; am impressed by Apple's integration of various devices and am just ready for an IT-change-of-scenery. Family needs a second laptop and I'm determined to get a Mac this time around...although the price tag is high (am familiar with the "bang for the buck" arguements).

Maybe someone can give brief purchasing advice to a Mac virgin?

Needs: Average office productivity; browsing; simple photo editing; need for video editing of AVCHD files; streaming of iTunes files from external HD to Airport Express; limited portability as I have a nifty IBM X60 which is great for bringing along (17" is too big though); ability to run XP for a handful of small applications for Windows only;

Looking at either a new MBP unibody 2,4 GHZ or an older (purchased Oct '08), unopened MBP 2,4 GHZ for about 400 USD less from a private seller. I would most likely max out the RAM and HDD myself when able. I usually prefer new things and like the feel of the MBP uni, but do I get anything other than aesthetics for that money?

A new MB is also an option, but I feel that for a relatively stationary machine I prefer a bigger screen. Don't know much about computers but dedicated graphics card in MBP sounds better.

Any comments?

A long post, but I don't know any Mac owners with deep IT knowledge.

i would definitly stay away from the base macbook with the plastic body, the built in graphics just don't quite do the trick

Actually all macbooks have the same integrated nVidia GeForce 9400M GPU. Personally I would go for the new Unibody MBP, as the 9600mGT is far better than the 8600M GPU of the older MBP. Also with the Unibody, you get the new Touchpad, which is awesome.

just go with the unibody mbp..because of the ddr3 and faster everything
oh btw new touchpad! which i dont prefer. just cant do the trick for me really..

Even the white plastic mac has dedicated graphics right now, the only one of its type to have that. I'd say that's a sweet buy for $950 if you have kids and can get education discount. Then again the new touchpad is sweet!

Having had both go with the alum. and don't look back.