You can replace the 7850 with the 6870 if you want.
You should d/l an English ISO disc of windows 7 and use the key.
Fill this form out for a more suitable build to be recommended for you.
1. What is your budget? [€xxx]
2. What will be the main purpose of the computer? [Gaming/Video editing/3D Modelling/HTPC/Internet] (If gaming include which games)
3. Do you need a copy of Windows? [Yes/No]
4. Can you use any parts from an old computer? [Hard drive/DVD Drive/Case/PSU/etc.] (If possible state brand and model of the parts to ensure compatibility)
5. Do you need a monitor? [Yes/No]
5a. If yes, what size do you need. [19'/20'/22'/24'/etc.]
5b. If no, what resolution is your current monitor and do you plan to upgrade in the near future? [1920x1080/1440x900/etc.] [Yes/No]
6. Do you need any of these peripherals? [Keyboard/Mouse/Wireless Card/Card Reader/Speakers/etc.]
7. Are you willing to try overclocking? [Yes/No]
8. How can you pay? [Bank Transfer/Credit Card/Laser]
9. When are you purchasing? [In x days]
10. If you need help building it, where are you based? [South Dublin City/Cork City/Kerry/etc.]