Originally Posted by DanRSturbo
You can buy the box seperately, and then ring Sky up and say you want the sky + service but you have sourced the box elsewhere

My neighbour did this last week

I did this too, you'll need to buy a DUAL or QUAD LNB too if you want to be able to record two things at once, or, watch one channel while you record another. They are around £15 on ebay and elsewhere.
Best get a Quad if you are planning on running two sky+ boxes, and they are not that much dearer if at all.
You'll also need a second run of satellite cable from the box to the dish. The DUAL or QUAD lnb effectively acts as two or four dishes at once.
HTH