Do you currently have a 9800GTX+?
If so, you can try the following:
1) Use your 9800GTX+ until you get more money. Yes, the 4890 is noticeably faster, but not very much. Probably around 15-20% faster. Which is not a whole lot, considering how much money you will spend on a new card. You may want to check out benchmarks to see how big the difference really is.
2) Sell your 9800GTX+ and use the extra cash to get a HD 5850. They were going for $270 or so a few weeks ago on newegg.com.
3)
You can give AMD Phenom 2s a try. Benchmark between Intel 920 and Phenom 2 965. The AMD Phenom 2 965 is a little slower than the Intel Core I7 920, but costs around $100 less at newegg.com. Look at the performance, is is not much slower.
So if you save $90-100, you can put that towards the 5850. That would make a faster overall PC for games.
Costs about $30 more than the Q8400, but as you can see, the Phenom 2 965 is faster than the Q9550. Which means it will most likely be considerably faster than the Q8400.
I think with the AMD CPU, you will have enough cash for a HD 5850 and get an overall more powerful PC.
Seems to be the better price/performance deal out of your Intel options. Plus, LGS 775 is dead. AMD3 socket is newer and will be around longer. They might eve release new CPUs in AMD, meaning you would be able to upgrade again. Can't do that with Intel.
I am happy with my AMD Phenom 1 9950 quad core, and this quite a bit faster.
Also, why are you going with a 32bit OS? You're just limiting yourself. You can't even use 4GB of RAM, and more programs in the future will use it.
I have been running Vista 64bit for around a year with almost zero issues.
Ok, interesting

So this would be good: AMD Phenom II X2 Dual Core 550 3.10GHz @ 3.30GHz Black Edition? This is only Dual Core though and the others are Quads, so how is this faster? EDIT: sorry just clicked on your link and you are referring to the X4 which is a Quad, so this one not so good? See below, found an X4 setup with an HD 5870...
The setupps I have posted previously are made up ones from OverclockersUK as I am not bothering building my own up anymore. The CPU I have just mentioned comes in this setup:
XFX ATI Radeon HD 4890 1GB GDDR5 Graphics Card
Gigabyte GA-MA790X-UD3P AMD 790X PCI-Express DDR2 Motherboard
AMD Phenom II X2 Dual Core 550 3.10GHz @ 3.30GHz Black Edition
Corsair TX 650W ATX SLi Compliant Power Supply
Seagate Barracuda 7200.12 500GB SATA-II 16MB Cache
Corsair XMS2 4GB (2x2GB) DDR2 PC2-8500C5 TwinX Dual Channel
Titan TTC-NK85TZ Fenrir CPU Cooler
Coolermaster Elite 334 Case - Black
High Definition 7.1 OnBoard Sound Card
Optical Drive LG GH22NS30 22x DVD±RW SATA Dual Layer ReWriter
which is considerably cheaper than the i7 setup and I would be able to change the 4890 for the HD 5850 and maybe an extra 6Gb of RAM or the 500Mb HD to 1Tb, I have £1k to spend but it's getting eaten up quite quickly on these builds lol.
And just searching further, found this:
- AMD Phenom II X4 Quad Core 955 Black Edition 3.20GHz Overclocked to 3.80GHz!
- Sapphire ATI HD 5870 1024Mb
- Gigabyte GA-MA790XT-UD4P (Socket AM3) PCI-Express DDR3 Motherboard
- Corsair XMS3 DHX 4GB (2x2GB) DDR3 1600C9DHX
- Gelid Silent Spirit CPU Cooler CPU Cooler
- Seagate Barracuda 7200.12 500GB SATA-II 16MB Cache - OEM
- LG CH08LS10 8x Blu-Ray Reader/16x DVD±RW - Black
- Coolermaster Elite 334 Case - Black
Just over my limit but worth the extra if it's good....? My head hurts now, so many choices!