What kind of trouble are you having?
I think that if you change the MX records to point to Google's mail servers you are pretty much stuck with using either Gmail web access or your computer's email client. I don't know of a way to have a single email account still flow to your domain's web space and be accessible via Horde, Roundcube or SquirrelMail if you change the MX records.
According to Google there is a way to point your MX records at their servers and then bounce unknown addresses (the ones that aren't set up in Gmail through Apps for business) back to your legacy mail server. So if you're managing a larger deployment of Google Apps across your organization you don't have to switch everyone all at once. In case something goes wrong...
I'll keep working on it. Thanks for the reply!