Um... Can you read your question and then explain it to me...
QUOTE(DangerousDave86 @ Jun 23 2007, 11:36)

I have an odd internet set-up at home. I have PC1->PC2->Router.
I'm assomeing there is a reason for this configuration existing in the first place ... What is/was it.
QUOTE
Now, the middle PC runs a proxy, for the second PC (Not ICS though, as 192.168.0.1 is taken - and while I could 'get it back' it would upset things out of my control).
Okay... If not ICS then what (This ties into the above's "Why are we "here"" question). Also 192.168.0.1 is takes by...? and what other networks are involved.
QUOTE
So could I add some sort of route to the middle box that allows it to forward requests to the router?

...If it's acting as a proxy for PC1 ... It kinda has to already have access to the (DGW) router. Giving it 2 paths to the (DGW) router would cause a conflict.
QUOTE
If I set PC1s gateway to that of the router, what route would I need to add to PC2 to get it to actually go to the router, and stop all the proxy nonsense.
Um... Fill in the blanks.
PC1 = IP____ <-> ___IP <-PC2-> IP___ <-> ___IP <-Router-> IP___(Internet...?