the voucher when you buy vista after the 26th is for a discount on win7, not for win7 so you'll still pay a good $100+ for win7 even with the voucher since win7 home premium costs something like $190 IIRC.
^ well that's the rumour of what was going to happen, but in the last couple of weeks someone came out and said that if they did offer a free upgrade then they would lose a good $100+ each sale, and since win7 is in high demand, they would lose millions in total.
It looks like a decent build to me, however I would get a CPU heatsink/cooler that is better than the stock. The stock is okay if you don't OC, but for best stability and later ability to push it farther, you will want a good cooler.
Other than that, it looks good. Have you tried out the Windows 7 RC yet? IF you are going to use it in the meantime just remember that you can't upgrade from the RC, it would be a full reinstall. It will upgrade from that install of Vista though.