That's what I'm doing. I'm *hoping* to buy a new PC (Core i7, ASUS MB), and plan to run 7. I've already checked with the companies that produce the software I use the most to make sure they'll run on 7, and got back affirmative replies, so I should be good.
Now when Diablo III comes out I should be good to go! Old Blue Bessie here will croak if I even attempt to install a program that big.
Best bet is just run whatever OS was shipped with the computer when new and install the updates and patches for that version;it will continue to run all the programs it originally ran.When you have new needs,then buy a new machine with the latest OS pre-installed;it will save you money and time.
Same basic principle applies to MacOS and others;as OS feature list grows so does requirement for more ,newer hardware.
I know of control systems now running on high-end P4 boxes that originally ran just as well on a Win 3.1 486 box.The production machine ,its sensors and motors simply don't require much computing power.
Americans spend a fortune replacing a lot of things that were still performing their functions economically.just to have bragging rights "I got a new "xxx".
bttt
If it ever comes out! grumble, grumble...