Best way to increase wireless network range

Hey all, This is the first time I have ever had to worry about this problem and I am downright clueless as to where to start. I recently moved into a new house where the router is upstairs and in the front of the house. My room is in the back and downstairs. Moving the router isn't really an option and I need network coverage back there for my law work. How can I extend the network for the least cost for the results. I can see the network but it seems to be incredibly low and goes in and out. Thank you all for your help in advance! If you need more information, please ask. The router is a WRT54G2 by linksys.

1) New antenna(s). Linksys sells some higher gain antennas for their routers and depending on the card in your computer you could put another on there as well.

2) Upgrade your firmware if possible to one of the third party firmwares. They usually let you increase signal strength.

3) move any objects in the way that may mess with the signal. Microwaves & large metal objects will kill your signal.

I think that adding an antenna is the best course of action. There are no antenna on the current model so adding one would seem to be the best route. Could anyone recommend one that would work with my router (see first post for model) that they know will work. My search for one gave too many options and I felt like I couldn't see the trees from the forest. Thank you!

You could look into a repeater. It is simple and easy to set up. I believe it would also be the most flexible inside of a home. Here is an example . There is other products about, and price points. They cost about the same as a router usually.

Link goes to what a repeater is:
http://www.wisegeek.com/what-is-a-network-repeater.htm

High-Gain antennas plus DD-WRT firmware if your router supports it - and your WRT54G V2 should support it (allows you to increase TX power - but don't go crazy or you'll have heat issues ~80-85mw is where I generally leave mine).

I used a repeater w/WDS, but I found that descent antennas and DD-WRT gave me the range I needed, and repeaters will decrease WiFi throughput (not really an issue for WAN bandwidth unless you have 50mbps internet service, but will slow down local LAN bandwidth). The WiFi cards in the Laptops or PC's also vary drastically with regard to sensitivity, TX power and such... If you do decide on a repeater, use the same brand and same chipset that is in your primary router for the best chance of success (I used a second WRT54G as a repeater in "WDS" mode running DD-WRT firmware - it did work, but I didn't end up needing it )

... directional antennas, chances are your running stock dipoles that send a signal out in every which way. and chances are your router is not in the center of your house, its probably in a corner.

i highly suggest simply making some parabolic slip on dishes they should do a good job and are gonna be essentially free. i cant find the link right now but i kno there is a template out there that you can scale to any size put some tinfoil on the parabola and you got yourself a directional antenna.

you could go super directional with something like a cantenna.... i was able to use a cantenna on my wrt54GL pointed to a pond ~ 1.5mi away, and use my wifi on my laptop at the pond using a parabolic dish, with ddwrt only up to 63mw output... you really shouldnt go much higher.

problem is that router doesnt have an external antenna.