May I ask why a laptop in particular? It just seems that if you stick with a rig, it'd be fine. What you are asking is really almost not cost efficient if you are buying a laptop but don't move around that often.
The only stores that do monthly payments are stores like Carrefour and MediaMarkt IIRC.
That's shooting yourself in the foot for choices btw.
There's also Paradigit but I don't think they have monthly payments.
There are more sites, but I wouldn't suggest using them. Hell, I would even suggest using mediamarkt or paradigit.
Their customer service is awfull.
btw, If you're really planning to buy a laptop and you're going to use it for gaming, don't work to buy a coolpad for it. You could also look into the MSI and Alienware mx series. A cheaper one which will even give you a i7 would be Acer.