The computer that is alone gets used fairly frequently for large uploads and that is why it was removed from the network (it slowed all of the other systems to a halt) but I would like to get it back into the network without affecting the others while it is uploading.
If it were me, I'd have that PC running on it's own highspeed connection and then share the other with the rest of the computers.
You don't need a twin WAN router to do this.
Here's how I'd do it.
Router 1:
IP: 192.168.0.250
Subnet Mask: 255.255.255.0
DHCP enabled - Scope: 192.168.0.100 to .200
Router 2
IP: 192.168.0.251
SM: 255.255.255.0
Default Gateway: 192.168.0.250
DHCP disabled
Give the one PC that you do all the dowloading with a Static IP that's not included in the DHCP scope. For example:
IP: 192.168.0.10
SM: 255.255.255.0
Gateway: 192.168.0.251 (router 2)
Let all other client's in your LAN get their info from DHCP from router 1. The DHCP scope should give out the 192.168.0.250 IP as the default gateway to all other clients.
Have router 1 plugged into the incoming internet connection and a crossover cable from a LAN port on it to a LAN port on router 2 and clients plugged into the ports on both routers.
You might have to go from LAN port on router 1 to the WAN port on router 2 in order to make it work correctly. I haven't tried this myself but have no doubt I could make it work.
This negates the need to buy any more equipment (except maybe a switch) and allows you to keep all clients on the same LAN and separate which DSL connection they use.