First of all: don't blame the router vendor or ISP!
The problem is with the way that Microsoft implemented "browsing" all those many years ago (BTW: "network neighborhood browsing" is not to be confused with "web browsing", which is a totally different thing). MS made the assumption that network browsing would be within the LAN...not over a WAN. And so they implemented it using Netbios. Now since Netbios is a non-routable protocol, it's gonna be a trifle difficult to browse across routers! Netbios relies on broadcasts to resolve network names. So you could enable Netbios broadcasts over your routers (maybe), but that's really not a good idea, and probably would cause you more grief than good.
The "supported" way is to have a WINS Server on every LAN segment, and have them replicate with each other. A WINS server can resolve Netbios names (typically, computer names or "share" names) to the associated network address. Basically, it "sniffs" the local network to get name to address mappings and then replicates this information to its partners.
OR, if there's a finite number of systems, you could configure an LMHOSTS file on each system and have Netbios name resolution use it (rather than broadcasting or using WINS).
Now you may have read that W2K was supposed to have solved this problem and no longer requires WINS. Well, yes and no. It is true that the W2K domain controllers no longer rely on WINS servers for their own domain-related stuff, as the NT4 ones did. But that doesn't mean that all the OTHER apps (like Windows Explorer!!!) don't still need a way of resolving Netbios names to network addresses. Until the whole suite of apps that use Netbios-based browsing are updated, we're going to have this problem.
If it were my call, I would put at least one W2K or XP system on each LAN segment, make it a WINS server, and be done with it (that's what I did).
Makes you wonder why someone like Linksys doesn't build a WINS server into their router; it would really make life simpler.