OT : help needed for a Apache 301 redirect using regex

[jbv at souslelogo.com]

Hello,
If there are any experts in 301 redirect using regex, please answer off-list.

I have several urls of this kind :
http://www.mydomain.com/foo.php?someName_someCode

that I need to permanently redirect to something like :
http://www.mydomain.com/?foo_someName_someCode

There are actually thousands of urls in which someName_someCode
is different, and I have troubles writing the regex for a 301 RewriteRule.
So any help would be much apreciated.

Thanks in advance.
jbv