I've been using WAMP to work with PHP. These days after joining PHP mailing list from php.org, I want to have a try on EasyPHP. Though I'm not confident to get on alone with EasyPHP :)
So my question is can WAMP and EasyPHP be installed the same time on Windows7 (or Ubuntu OS)?
Yes, they can. You might take a performance hit from running both OSes at once (which you can do using a VM), but as long as you don't try to make them share resources (e.g. ports and config files), they won't even know the other exists.