Assuming you purchased recently, the Linksys model is most likely WRT54G.
There are two ways to attack this:
1) A cable handling the link between routers (router as an access point)
2) Wirelessly via WDS (Wireless Distribution Service)
Each method has benefits and drawbacks:
The AP method is the simplest to do and offers the best speed, but the cable might pose aesthetic issues.
WDS needs no cable, but requires tinkering with the firmware on at least one router, and also suffers a loss of throughput. Note that you will also void your warranty by altering the firmware.
Method One (easy)
Configure R2 as an access point.
1-*Connect the cable from R1′s ports labeled 1-4 to the same on R2.
Do not use #4 if labeled “Uplink” on R1. Use #4 on R2 if it does say that.
2-Attach a computer to a second port on R2 and access the configuration (usu. 192.168.1.1 in your browser)
3-Change R2′s password immediately just for security.
4-Change R2′s IP address to one on the same network (if R1 is 192.168.1.1 try 192.168.1.2)
5-Disable DHCP if it has the option, choose “Router” over “Gateway” otherwise.
6-Configure R2′s wireless to MATCH R1.
*Step 1 can be done at the beginning or the end in case you have a limited number of wired devices.
Method Two (hard for beginners and voids warranty)
Set up WDS by replacing the firmware on R1 (and maybe R2)
1-Replace the firmware with one that allows you to use WDS
You will need to do some searching on which to use and how to install, there are several variants.
Determine your hardware version <i>first</i>, as not all firmware is compatible!
The danger here is that you may ‘brick’ your router replacing the firmware…
Configuration my vary greatly between each firmware variant.
2- Set up WDS on R2 if it becomes available (Linksys supposedly slipped in support for WDS recently)
If not, you’ll need to replace the firmware on R2 also.
If you want suggestions on WDS, try joining a technical chat room to get opinions of people who have tried it.
Some prefer a specific firmware replacement, and may offer insight into how difficult the process is.
Unfortunately, it is difficult to offer more advice on such without knowing more about your hardware.
Wikipedia on the WRT54G. The section about third party projects should give you links to most available firmware. They should have enough documentation to make a determination on your own.