My wireless internet is a bit choppy because of a floor difference, how can I improve this?

Most wireless routers default to channel 1, 6 or 11, so if there are other networks nearby they could be interfering. Cordless phones usually start at channel 1 and switch channels to get a better signal if necessary. Microwave ovens put out interference mostly on channels 7-11. If the disconnects happen when the phone or microwave is used or when people get home from work, that's a clue. I find channel 4 works well in most cases. And remember to change the default SSID and router password and enable WPA encryption on your network.

You can run a cable down to your machine, or buy a bridge and mount it closer to your router (like on the ceiling).

Or you can switch to the new wireless band called N.

N band, can support a network for over 300 yards on the ground, or between 10 cement floors.

Make sure you're configured to use 802.11g, not 802.11b, because g has more range than b. You didn't say what type of Linksys router you have...