Yesterday, Microsoft announced the upgrade and normal pricing for Windows 7 which goes on sale October 22.
Starting on Friday, June 26-July 11, a limited number of Windows 7 Home Premium upgrades will be sold for $49 and Windows 7 Professional for $99.
Upgrade prices will be $119 for Windows 7 Home Premium, $199 for Professional, and $219 for Ultimate when released in October.
Normally, I recommend not upgrading to a new version of Windows on an older computer. If, however, you have a computer that you purchased in the last two years and it has at least 3GB of RAM, an upgrade to Windows 7 from Vista may be worth it.