Yes, but you can only do an in-place upgrade to Windows 7 RC from Vista SP1 or SP2, the latter still in RC form itself.
What edition of Windows 7 is the release candidate?
The RC is the Ultimate edition of Windows 7, the most expensive of the line.
What languages are supported?
Microsoft has limited the RC to English, French, German, Japanese and Spanish. Arabic and Hindi, which were available in January's beta (though Hindi only in 32-bit) were dropped in favor of French and Spanish.
Can I upgrade from Windows XP?
Although Microsoft will sell Windows 7 "upgrades" to XP users, it's just a version term for them, allowing them to buy the new OS at a lower price. When Windows 7 goes final, XP users will have to do a "clean install" that erases the contents of the drive; the same goes for the RC.
To transfer files and settings from XP to the new Windows 7, use the Easy Transfer utility included with Windows 7 RC. After you've burned the downloaded .iso file to a DVD, insert it in the XP machine's drive and copy Easy Transfer to the PC. When you run it, Easy Transfer will copy files and settings to an external device -- a USB flash drive comes in handy here -- which you can then copy to the PC after you've done the Windows 7 RC clean install.
Does Microsoft provide support for Windows 7 RC?
Microsoft doesn't do technical support for pre-release software, so your only support option as an RC freeloader is online, in the user-to-user forums.
When does the release candidate expire?
Microsoft pushed out the expiration date for RC to June 1, 2010, nearly 13 months from its debut, significantly longer than the "free" time frame the company gave users for Vista.
On that date, the release candidate will stop working, but you'll get plenty of advance notice. According to Microsoft, Windows 7 RC will start automatically shutting down at two-hour intervals beginning March 1, 2010.
By the way, if you stick with the beta, remember that it expires much sooner, on Aug. 1, 2009, with bi-hourly shutdowns starting July 1. In each case, Windows 7 will remind you two weeks before the shutdowns begin that the beta or release candidate expiration process is about to start.