My thoughts - Is there any feature in Vista Ultimate you really want compared to Home Premium? Unlikely so ditch it and use the extra £150 for the faster processor or blu-ray.

Screen resolution this is more complex choice than you think. If your a gamer go for 1280x800 if you will watch HD movies or need hi-res for graphic work then go for the highest res. Why? The graphics card is capable of playing most games at 1280x800 (with med/high settings) so you will see them in their native resoultion on the screen - i.e. 1 pixel lines up with 1 pixel and the image looks great. With a higher res screen the game will play choppy/laggy at hi-res and at 1280x800 the picture will look worse because it is being downscaled rather than running at native. For HD movies if you want to view on full HD 1920x1080 you need the higher res screen. As I think 720p (1280x720) is sharp enough for a 15inch screen and I export my picture via HDMI onto a TV when I want to watch full HD I go for the lower res screen so I can have better gaming.

Processor - I notice very little difference between a 2.4ghz and a 2.2ghz processor but defintely notice the difference between a 1.88 and a 2.13ghz processor so I'd say as long as you over 2.0Ghz don't worry too much about an extra 0.2ghz - however I went for the T7500 because I had the 2.13 Ghz on my old laptop and wanted my new one to surpass it in every way so that I would feel good about my new system.

I think the audigy is software not hardware. I heard that Vista doesn't support direct sound so direct sound effects in games are lost and the Audigy software restores those missing effects plus provides other enhancements to general audio. I think the sound on the 1530 even without this software is excellent whether you use headphones, surround sound (analogue or digital) or even the builtin speakers. I might get the audigy software later but it's not a big deal to leave this.