You seem to be slightly confused here. The XPS M1330 is an older laptop while the Studio XPS 13 is an entirely different model. I suggest staying away from the M1330 due to the well known nvidia GPU issue for which the company was sued last week.

Assuming you need opinions on the HP vs Studio XPS 13:

1. The P8600 is much faster and a lot cooler due the lower TDP which should result in longer battery life.
2. Not a hell lot in terms of performance at the moment. Cost is obviously a slight issue but it shouldn't matter in the long run since prices of DDR3 sticks are falling like gravity.
3. The XPS doesn't really have a "GF 9500" card but rather two lesser cards, a 9200M GS discrete and 9400M G on-board cards working together in SLI. So think of it as the HP card + a 9400M for a slight performance boost. Note that hybrid SLI is not supported under WinXP, so you won't be able to use that OS in the XPS.
4. What are the options that you're considering? BT, memory card reader, more RAM, faster processor?