Which wireless card?

[#1]

I am currently using the built in wireless card which came with the desktop but only get half the speed and consistent signal.  I am using a Dell Vostro and the wireless network card is broadcom 802.11g in device manager.
Would a new wireless card help with the connection and speeds and if so which one do I get? I'm no expert with these sorts of things but guess I would need wireless n???  Don't want to spend too much if possible but want to connect as reliably and fast as possible to the plusnet unlimited.  I can get speeds of 17mbps on ipad and notebook but barely getting 5mbps on desktop

[#2]

A new usb 'n' wifi card would probably help, they can be had for a few £'s on ebay.

[#3]

Yes it would help do you know if its a mini pic-e card in it, or what is the exact vostro model reason I ask is I have a spare atheros n card

[#4]

One thing that is often overlooked is obstruction of reception by the case.
Does the aerial have clear line-of-sight to the wireless base?
I try to buy internal cards that have aerials on a lead so that they can be positioned clear of obstructions.
If none of that applies and a USB "n" device is what you're after my personal favourite at present is the EdiMax EW-7711UAN.
This is quite small and comes with a short semi-rigid extension lead (not generally shown in sales information) allowing a degree of repositioning.
Note that there are several variants with similar names, here is that exact one from a typical eBay seller: http://www.ebay.co.uk/itm/330797034041?

[#5]

Quote from: thomasjc1

Yes it would help do you know if its a mini pic-e card in it, or what is the exact vostro model reason I ask is I have a spare atheros n card

Its a Dell Vostro 400 desktop.  I haven't opened it up yet so not sure if I need a mini card or standard

[#6]

Should have a selection of PCI and PCIe slots so it will depend which are used/free at present.

[#7]

well if its any use its a atheros ar5b93 half size pci-e card