Xircom CEM56: Slow network & other weirdness

[Evangelion]

I have a Xircom CEM56 PCMCIA-network-card/modem on my laptop. I works well when I use it with my broadband-access. At most, I get stuff at speeds of around 100KB/sec, which is how it should be (it's a 1MB ADSL). But when I access my other workstation throuhg Samba (it's a Windows-machine) I can download files from that machine at 100KB/sec at most. Both machines are connected to same 100MB switch, so there shouldn't be any problems there.

On a whim I tried to bring my network down and back up again, so I did this:

ifconfig eth0 down
ifconfig eth0 up

I then tried to download files from the other workstation, and I got speeds of around 500-700KB/sec, which looks alot better! All is well then? Not quite.... For some reason my internet didn't work anymore! I couldn't ping any websites, nor could I ping any of my nameservers.

So I basically have two questions:

A) Why is my network so slow when I access my other workstation?
B) Why didn't my internet-access work anymore when I brought my network down and back up again (which fixed the issue A))?
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