@scouser75:
Just be careful to keep an eye on the original .mac account. Gmail does not take kindly to bulk forwarding
to one of their email addresses. It's often a tactic used in spamming so they tend to reject the mail. Whether they do so really depends at what stage of the mail delivery the forward occurs (there's a lot of behind-the-scenes stuff involved).
Anyway, I mention this because the .mac is used for business so you'll want to make sure you don't forward
and delete, that way you can check the original account for a bit.
Another way to do this (that I found works better), is to setup Gmail to poll the .mac account. If .mac supports POP or IMAP connections you could have Gmail pull the mail in. It won't be instantaneous (its fetching frequency is dynamic and depends on the amount of mail you regularly get, but I think it's at least once an hour) and you will have to give Gmail your credentials for .mac (can you set per-application passwords? I don't know) so that might be a deal-breaker (it would be for me).