Routers/Modems Help

Our current modem/router combo box that sky gave us has random ping spikes and such, and its signal won't reach aaaaaaaaaaaaall the way across the house, my dad proposed buying a wifi extender, but I'd like something to fix the problem. Would a new modem or router be a good idea? Modems and routers arent exactly my forte, so im unsure which would be better, I would assume a router since we need a better signal.
Thanks for any replies! 

ya I would reccomend using a separate modem and router my experiance is that the all in one modem routers are not that good.  I would check and see what modems are compatible with your service and if you need a dsl or cable modem.  Then I would look at some routers I would recommend This I have used it and it works really well you can also look into getting routers that support DD-WRT if you want to go a bit more advanced and it will actually allow you to turn up the signal output.  This one will work well with ddwrt

i have a thomson tg585v8 from my isp and has wireless N, however the signal wasn't very god and very inconsistent when transferring files from my pc to my phone (vlc wifi upload) or using some type of vnc (like splashtop), i had a linksys wrt-45g laying around and plug it (it only has wireless g), it is way better signal and faster but not perfect, i still cant reach all of my house, but my house is of concrete and double brick walls.

probably you will need a good router and a wifi extender if you can, but having a good router makes a lot of difference, i will go for the router first, but a good one.

ps. the linksys is plug in the thomson, haven't try any game or voice server so i still don't know how the port forward has to be made but i will try later, but everything works fine, my linksys has dd-wrt in it. i still have the wireless ON in the thomson for when i have to mess around with the connection (i cant access the interface from the thomson when connected to the linksys) just use different channels and you will be fine.