I replaced my VCU by myself today - it's possible to do it yourself, but easier with 2 pairs of hands.
I didn't bother jacking the car up or anything, just undid both propshafts first and supported them on a few peices of wood.
Then put a trolley jack under the VCU to take the weight whilst the bolts are undone and then let the jack down VERY slowly. Whilst the VCU is going down, remove a block of wood at a time from under the prop ends until it's at the bottom of the trolley jack.
Then take a bit of rope and tie to each end of the assembly with enough to go around your shoulders. Pick the VCU up in the centre and set the rope to take the strain of the propshafts (rope is over shoulders) thus keeping the whole unit level...
To be honest, I don't think its that critical about keeping the whole assembly level - the only joint you need to be careful with is the front CV joint - the others are standard UJ's and the UJ will bind against itself stopping the bearings moving too far.
Hope this helps
d