Many sites that force users to register or even pay in order to search and use their content, leave a backdoor open for the Googlebot, because a prominent presence in Google searches is known to generate sales leads, site hits and exposure.
Examples of such sites are Windows Magazine, .Net Magazine, Nature, and many, many newspapers around the globe.
How then, can you disguise yourself as a Googlebot? Quite simple: by changing your browser's User Agent. Copy the following code segment and paste it into a fresh notepad file. Save it as Useragent.reg and merge it into your registry.

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\5.0\User Agent]
@="Googlebot/2.1"
"Compatible"="+http://www.googlebot.com/bot.html"

You're done!

You may always change it back again.... I know only one site that uses you User Agent to establish your eligability to use its services, and that's the Windows Update site...
To restore the IE6 User Agent, save the following code to NormalAgent.reg and merge with your registry:

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\5.0\User Agent]
@="Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)"