I would be hesitant of ordering in late November for Xmas. It should be ok but you must realise, hence your question, that many people may do the same thing.
If its a standard PC and the parts are readily available then there shouldn't be a problem but things do happen out with the control of the PC builder.
If in doubt then perhaps look at the likes of PC Worlds ready buit branded PCs as you can buy one there and then and walk out with it.
Whatever you buy though make sure it has either an AGP slot or a PCI Express slot for the graphics as I feel rather sorry for people who buy a lovely PC only to find it won't play a game and the graphics are stuck to onboard.