New Computer Time

Okay, so I want a new computer - I want FAST, small form factor, and will be using my current HD and DVDRW - main uses will be UD/ Seti/ Photoshop/ Gaming. (I intend to get a Radeon 9700/9800 256mb card or something similar) But I'm stuck on what CPU/mobo/system combination - here's the options from cheapest to most expensive:

System1 - Pentium 4 3.2ghz / ASUS mobo small form factor cube (socket 478 - so no upgrade potential) / 1gb ram
Total price around £300

System2 - AMD 64 3500 (2.2ghz) / Shuttle Nforce3 small form factor cube (socket 939 - so plenty of upgrade potential, even the possibility of dual core AMD chips... and will be able to run Windows 64bit) / 1gb ram.
Total price around £460

Edit - Found this system (using a QBic EQ3901A barebones cube) for £371 inc vat so am gonna get this system with an AMD64 3500.

System3 - Dual Core 2.8ghz P4 (Windows see 2 processors as it's 2 cpus in the space of one cpu - lots of heat though) / ASUS/Abit ATX mobo (intel 955 chipset) / 1gb DDR2 Ram / ATX midi tower case (would prefer small form factor, but dual core chipset isn't available in small form factor yet).
Total price around £508

System4 - Pentium M 2ghz / Commel Mini-ITX motherboard / 1gb DDR2 RAM
Total price around £610 (excluding case as I'll be able to use my current case) - Found a cube system for £199 (AOpen EY855) so the total for this would be £581 (still too much!)

What are your thoughts? The AMD seems the best: most future proof, 64bit capable, performance is better than P4 3.2ghz, heat output is less than P4s...

or I could get 10 x 1ghz P3 computers for £350 - then I'd have the equivalent of 10ghz :)