Well, Samsung make quite a few boxes for Virgin/NThell and only one or two of them don't follow international IR standards. MCE uses IIRC, IR6, so you really do need a compatible stb for it to work. The only way to find out (as virgin won't have a clue) is to set the box up via wmc set up screens. As I recall, the set up asks you to punch in a few channel changes/characters & from this wmc 'learns' the code set for the given box.
An IR cable & blaster is only a tenner or so, but you should really have had it in with the PC if it came from PC world. If not, I would go back & complain, since media centre is designed specifically to work with the microsoft remote - I would be surprised if it was sold without it.
One word of warning - the IR blasters can become upset if you use more than one remote, so for sanity, once it's set up, ditch the tv remote, get up out of bed to turn the telly on & off and stick with the microsoft remote.
It's hassle at the outset, but once you've got telly, music, videos, pictures & streaming media all one one remote, you'll love it. I'v just built my third media centre pc & I wouldn't have it any other way now. Good luck!
Edit: Just noticed where you are - I'm round the corner! The PC world I suspect you use, is IMHO, absolute rubbish, so if your pc is from there, go back & moan. BTW if you do use the tuner card instead of the stb, choose Midhurst over Whitehawk Hill - more channels!