Need some advice on upgrading a laptop

Hey guys 2 years ago I got a HP Pavilion zd8000 laptop before I got to college. I love the mobility, but now its obvioiusly outdated and I was wondering if it is worth upgrading or if I should sell it and build a tower with a lot more power.

Correct me if I'm wrong but does this laptop have a desktop CPU in it?

Currently the specs are:
- Microsoft Windows XP Professional
- Intel Pentium 4 520 w/HT Technology, 2.8GHz
- 17.0" WXGA+ BrightView Wide Viewing (1440x900)
- 1.0GB DDR2 SDRAM, 533MHz (2x512MB)
- 60 GB 5400 RPM Hard Drive
- DVD/CD-RW Combo Drive
- 256MB ATI Mobility Radeon X600
- 54g 802.11b/g WLAN w/ 125HSM/SpeedBooster
- 12 Cell Lithium Ion Battery

So what would be worth upgrading?
- 2GB of RAM - how much preformance would I gain by just doing this?
- GPU - anyone know of any good laptop GPUs?
- Would upgrading the CPU be out of the question?

Is it even possible could I put a Core2 Duo Processor in it? Pretty sure I would need a new motherboard (lga775)? And if my current processor is a desktop processor could I put something like a E6600 in it?

What would I have to do to get crysis to run on this laptop?

Sorry for so many questions, I know nothing about laptops. I do have a system in a wishlist on newegg if I can sell this thing though...

I wouldn't call it outdated for "normal" use. Replacing one of the 512MB RAM modules with a 1GB module to have 1.5GB total will definitely help in running Windows, and should be fairly cheap. Upgrading to a 7200rpm drive will help noticeably, but isn't cost-effective. A CPU upgrade is not practical on almost all notebooks. You might be able to "upgrade" the graphics with a plug-in card, but that is likely to be prohibitively expensive, too.

If you can't run your game(s), restore the notebook to as close to "new" condition as possible (clean the keyboard and screen, dig out the shipping box, manuals, accessories, etc), then put it up for sale.