Cheap and Cheerful graphics card

hey all.
sometime in late 2009 i intend on purchasing a rather nice laptop but until then i want to make some very cheap upgrades to my old rig to let me play games like fallout 3 and Empire: Total War.
the main limiting factor at the moment is my weak geforce 6200 gfx card.
i want to get a cheapish upgrade (maybe around the £40-50 mark)but i have a problem that the psu i have is only 300W (and before someone tells me to upgrade that aswell i want to keep costs to a minimum and because i have a HP and i think the psu case/area in them is different size to other psus)
i was wondering what graphics cards cost around that much and would be alright with a 300W psu. i have a pci-e slot i do believe but when it comes to hardware im quite a novice.
ive been suggested to buy one of these:
http://www.ebuyer.com/product/151344
http://www.ebuyer.com/product/126987
http://www.ebuyer.com/product/140617
the last of which seems to be significantly better according to the charts on this site but requires 'one X16 lane graphics slot available on the motherboard', and i have no idea how to check if i have one or even what one is.
are these gfx cards the ones i should be looking at?
and how do i know if i have a X16 lane slot thingy on my motherboard?
thanks for any responses