Upgrade on 2 rigs and possibly to win 7, help please

[Skarth]

I am hoping someone could advise me on the best upgrades possible on my 2 rigs, I used to just visit OC every few years and buy a new system but times are a bit harder now and funds limited to £500 max, but if possible much less.
I have a Dell S2409WB monitor for each machine and good Cooler master cases, PSU’S, keyboards, mouse etc, so am only looking to change the main components listed.
Another option would be to get further into over clocking (if my bits are worth utilising), as at the moment the only clocking is Rig1 Cpu running at 3114 MHz using Asus AI software.
The current components are
Rig 1 Running Vista

mb ASUS P5W DH Deluxe
cpu Intel core 2 duo E6600
memory 4mb ddr2 PC2-6400 (400 MHz)
gpu Radeon HD 4870 512MB
Monitor Dell S2409WB @1920 x 1080

Rig 2 Running XP

mb ASUS A8R-MVP
cpu AMD Athlon 64 x2 4200+
memory 2MB ddr PC3200
gpu Radeon X1950 512MB
Monitor Dell S2409WB @1920 x 1080


I use Rig 1 mostly for gaming (all the latest at 1920 x 1080 , while downloading/watching films/occasional World of Warcraft on Rig 2.
I need them both to be stable and upgrade both to Win 7 as soon as funds allow.
Thanks in advance for any assistance given

 

[Mercutio]

Well, for one of them the win 7 pro upgrade pack from a student software site is about £40. If you have a mate who could help, theres 2
I used to be a student in sheffield so stuck that down as my current details and had no issue from them.

 

[Skarth]

awesome, i will try that thanks

 

[Skarth]

any other suggestins ?