asp.net, frames with paegs from different servers

Hi,
I have this issue: I developed an asp.net application, it works, fine.

I have to place it inside an already-done frame:

--------------------------
server 1
--------------------------
S -
E - Server 2
R -
V -
E -
R -
-
1 -
-
-

The scheme should give the correct idea: server 2 is my hosted
application.
The issue is that css, javascript etc don't work basically because the
resource linked are searched in the "server 1" uri.

this is the example code:

<link rel="stylesheet" href="~/CSS/default.css" type="text/css" />
(dont' work)

<link rel="stylesheet" href="http://machine1/CSS/default.css" type="text/
css" />
(work)


but I can't resolve using this solution, because "machine1" is dinamic
and change due to load balancing

There is some quirks that I miss? some parameter in the containing frame?
HELP ME!