I'm getting married on 27th sept 08. Its only a small venue but I've set my heart on it even though I'm struggling to fit everyone in. it would be a huge help if I knew who exactly will be able to attend especially so I know how many to cater for. When is an appropriate time to send out invites and ask for rsvp's by without sounding pushy? X

If it could be a struggle to fit everyone, you'll have to either cut the guest list or find a new place.

Invites should be sent out only 8 weeks before the wedding, and ask that RSVP's be returned 3-4 weeks before the big day.
You want to be SURE you're space will fit the entire guest list though... some people may not RSVP, but they'll show up anyway!

I've had friends mail out "save the date" cards to friends and family months before the wedding. That way, they let people know way ahead of time of the date.

Here's a few sites:
Save The Date Wording - Save The Date Ideas - Save The Date Examples
Save The Date Cards, Save The Date Invitations, Wedding Announcements

Oh, and congrats, sweetie! :)

Thanks, I really like the save the date idea! Never thought of that, thanks again x