http://ww2.nero.com/nero6/eng/Nero_MD5_Verifier.html
Paste the MD5 Checksum for either x64 or x86 depending on which one you want
to
check in Step 1, Step 2 - Browse to where you stored the ISO on your drive
and open it and it will automatically start the verification process and
generate the result in the third field, if it matches Step 1, then you are
safe.
I have written a MD5 checker speficially for Vista, has the official MD5's
included with it, do it's a select the version (currently RC1 32bit, or
RC1 64bit), point it at the downloaded ISO, and click Check.