wireless routers will work for any wifi compatable device bascially .... so probably any wireless router u get will work....
if you don know this already a router basically splits your internet connection is multiple connections that are shared between any device that connects to it... you will have to connect your DSL modem into the wireless router via a wired connection and then set up the wireless connection with the other devices.
the only effect it may have on your exisiting network (considering you only have one device on the network) is that the speed will decrease depending on how many devices you have connected and how much bandwidth the devices use.
for more info please go here and search "wireless router"
also note that because nintendo uses "nintendo wifi connect" some ppl experience difficulty based on the security features of the router (for more information on this please go to www.nintendo.com --> support) for a list of routers that work well with the wii.
just to reiterate, 98% of all routers out there work with both wii, and psp, as well as the ds, PS3 etc...