I suggest you read the Motorola 6141 manual, commonly available on the internet and I've uploaded a copy above, it'll answer many of your questions.... Blue colored LEDs mean bonded channels or GigE connection depending on which LED you're looking at. If send/receive LEDs are green colored that means single channel lock. An amber link LED means 10/100 ethernet connection. The new shape allows it to be laid down on it's side without looking odd and wall hanging without a homemade mounting bracket. The modems are international, so no need to make separately printed LED labels in other languages like the 5100s and earlier needed, one model can serve all countries as far as I know.
Ok, you have the PC plugged into the router and the router plugged into the modem. The PC is getting a IP from the router right? Something probably in the 192.168.x.1-255 range right? If it's getting an IP in that range, it's getting it from the router not the modem since it's no longer a combo router modem. If it's getting the IP from the router, it's getting the lease time from the router, that's the way DHCP works. If the router is set to pass on the DHCP parameters received by the modem, instead of creating it's own, that's another router config issue, but in that case your Win8 machine would be getting a public IP if it's able to access the internet. Tell us how it's not the router if that is what your PC is connected to?
The interconnection between your XP machine and Win8 machine is handled by your router. The modem shouldn't even see any of that traffic. So the machines not seeing each other is either a PC config issue or router issue.
You'd be able to check all of this if you had access to your own router, but you still don't know the password do you? Don't give us the story about why you can't access it again...
 For those who want the story on Mele20's router password issue:
2007: »[Wired] BEFSR41 v3 password suddenly rejected
2008: »Re: Raising Awareness: Another CSRF Attack (Linksys)
2009: »Re: New PC Advice?
2010: »Re: Call up: change the default password on your home router
2012: »[TWC] No more perboost?
We won't go into the DHCP problems you know that particular router has... it's obviously a LONG time, sore subject.
Without testing against another router, testing without a router, or seeing what the router is currently configured for, your router is the mostly likely suspect in your PC DHCP lease issues.
[edit again]You can hard reset your router and setup the password again without losing the beta firmware on it, but if you really are worried about it you can get a copy of the beta BEFSR41V3_v1.06.05_000_code.bin firmware here: »Re: [ENG] TM402P reset--
If it's important, back it up... twice. Even 99.999% availability isn't enough sometimes.