Connection awfully slow

[mdi]

Hi, I'm quite new to Linux but I decided to install Gentoo anyway. My problem is that, even though I have a reasonable connection, I'm only downloading 2-5kb/s when running Linux.
My connection is an ISDN128 connecting to the internet with a router. In Windows I almost always downloaded with 14-16kb/s, but Linux (Gentoo and RedHat 9) only gives me a download speed of 2-5kb/s. I have set my eth0 network card with the right IPs, subnet, gateway, DNS, so the only thing I'm not quite sure how to set is the broadcast adress. I've tried experimenting a little, but it didn't change anything.

Does someone know what causes this extreme drop in performance? I've read a lot of the posts on this board, but I haven't found anything which helpes me.
Hope one of you knows whats wrong. Thanks in advance.