If it's compatible with a router, it must be compatible with a Mac. Try their FAQ.
Yes, as the poster above suggests, you could try RTFM! I did it for you....
From the Virgin.net website:What will I need?
Minimum Mac requirements:
PowerPC 601 or equivalent
200Mhz
32 MB
Two-speed CD-ROM player
Video driver/display 800 x 600, 256 colours
100 MB free on hard drive
Mac OS 8.6-9.2, 10.1-10.4 (Mac OS 10.0 is not supported).
There is currently no driver support for Intel based Macs.
Spare USB port
This is related to my post above - it looks like the package comes with a USB modem and that there are no drivers available for it yet for Macbooks. Which means that out of the box it won't work.
However, as I said, you won't want to use the modem they send you anyway, as it defeats the object of having a portable, so you could easily buy a cheap wireless modem/router to replace it - they're start at about £50.
Or try another broadband provider....