Is your car 3 stud? Because if it is that'll make it quite an issue to fit them!
If not Saxo's are 4x108 and most BBS's available seem to be 4x100 so you'll need adaptors to bolt them on, but when you fit adaptors they also space the wheels out so you need to make sure the initial offset is that, so they sit right with the adaptors.
The other option you've got (which is what we did) is get the wheels re drilled to fit your car.
There are BBS's out there with the correct offset and stud pattern etc but all BBS (RS's at least) were oe wheels, and not available as after market wheels so you have to pick wheels off another car that will fit yours (mine are off a Lancia Delta Intergrali)
There are BBS lists out there giving you the model number, stud pattern, offset and the original car they are off out there, but everyting depends entirely on whats for sale (on eBay) at the time.
Good luck with all this