Merkuri
Explorer
I don't have a middle mouse button. I browse the forums on a PowerBook G4, which I should also add does not have a right mouse button either, for that matter.
Oh, hmm... I'm not as familiar with Macs, but there's probably a key combination you can use. I know in FireFox you can do ctrl-left-click to open it a new tab instead of the middle button. Maybe you can apple-click links to open them in new tabs?