You'll probably find that a 9-pin to 9-pin "Null Modem Cable" is what you'll need to connect to most non-cisco equipment.
For a 25-pin to 25-pin Serial connect, you could probably get away without a full cable, as follows:
1 ----- 1
2 ----- 2
3 ----- 3
7 ----- 7
4 \ / 4
5 / \ 5
6 \ / 6
8 - - 8
20 / \ 20
This is supposed to show 1,2,3 and 7 straight through, 4 and 5 looped at each local end, and 6,8, and 20 looped at each local end.
You could try crossing 2 and 3 if this doesn't work. Depends on whether the devices are DTE/DCE.
Of course it would be much easier (if the devices had been set up correctly) to TELNET in to their IP address!
Hope this Helps...
Jason.