Switching to an i7 920 is not possible with some of your parts...
First off the i7 is a different socket type than the i5 so that means it won't fit into your MB.
Second... i7 MB's use triple channel memory (3 x 2gig sticks) so your memory won't work either.
The 275 will fit as well as the 700W PSU.
Question for you with the HD... what are you going to be storing on it? 2x1TB in Raid would be faster but you have the chance that all your data could be lost if one drive dies...
Overall, if you want to get an i7 just wait and I would go that route... look for combo deals and save money. On the other hand the build you have listed is pretty good though you won't be able to use the MB and RAM if you want to upgrade to an i7...