Right, well i have a 17" 1.83ghz intel core duo imac, which is irrelevant i guess and im getting a samsung t220HD which will be used as an external monitor and my ps3 will be running threw it, ill also be getting m-audio BX5A deluxe active monitors. now first of all im going to be connecting my imac to the display from mini dvi to hdmi, which is all fine, but with my speakers how can i connect them to my mac and my external monitor and what do i need..sorry if this is not clear enough any questions just ask and thanks!

From what i can tell from m-audio's site, you plug a stereo trs connection into the back of one speaker (which i assume then feeds the second speaker).
If thats the case all you need is trs male to trs male connector, one end will plug into your sound card (or onboard) analog stereo output, and the other will plug into the main speaker.

Edit: Since you're on an imac you'll need to hook it up the the headphone output on the back side of the mac. This seems to be the only output they offer. If this doesn't work well you can always buy a usb sound card.