[DanL]

You can't link two routers like that unless the router is specifically designed to work like that (which most consumer routers aren't).

If, on the other hand, you wanted to use that second router to extend your wireless network coverage - have two wireless routers on your network - that is possible, but you have to wire the two together. In this case, one is acting essentially as a wireless switch or hub. If you were to do this, first of all, you ignore your secondary router's (the one NOT connected to the cable modem) WAN port - connect the two using their LAN ports. Second, enable DHCP only on your primary router (otherwise, you have the two routers fighting for supremecy and you end up with problems). Disable it on your secondary router, and assign it a static ip outside your DHCP range. For example:
primary router (DHCP server): 192.168.0.1
secondary router (DHCP disabled): 192.168.0.2
DHCP range: 192.168.0.100 - 192.168.0.105

Again, this isn't what you're looking for since you have to physically connect the two routers, but if you want to extend your wireless network using the second router as a wireless switch, this is how you do it.

Wireless Security Hints:
1. When using DHCP, don't make the ip range any longer than it needs to be - i.e. if you have two computers at your house, make the DHCP range contain 3 addresses. The logic behind this is its one way to stop the casual wireless network sniffers while leaving some room for expansion (i.e. friend brings his laptop over). And wireless network sniffers aren't an urban-only problem... even in suburbia, bored techies drive around aimlessly looking for open networks (trust me - my brother has successfully done it)
2. Change your router's password from the default - any hacker worth the title knows all manufacter's default passwords
3. Change your wireless configuration's default password (depending on the make, you may not have a seperate password for wireless settings)
4. Enable atleast basic WAP again, to stop the casual network sniffer