Low local transfer on WRT54GL router

Hi,

I encounter small problem with my WRT54GL router with Tomato firmware
1.21. Router is connected to Internet via Cable modem. I have 3 devices
connected to this router - all of them via wireless connection. On one
laptop (Windows XP Professional) I have FTP server (guildftp) plus emule
and I think that's all. On other laptop there is Windows Vista Basic and
I’m using this for simple internet - www, IM. And third device is
Iphone, which is connected all the time, but data transmission is used
only occasionally. No firewalls installed and active on any of the
laptops. On one I have local, polish, arcabit antivirus software, on
second home version of Avast. Nothing else. I’m having this
configuration for some time, but I remember when I had other PC with
Windows XP and Windows Vista Basic – it was exactly the same ( I had
them only for a while, so I didn’t think about that at all)
And the problem i have is with transfer data between laptops – I’m
trying to download anything from laptop with Windows XP, through FTP
using Total Commander I get transfer at 5 KB/s – and it takes ages to
download anything. Pinging each computer causes about 1/3 of pings not
to be returned. PCs are close to router, from both of his sides.
Connection to Internet works perfectly fine – on both laptops I get full
Cable modem speed, downloading and WWW works fantastic. Only
transferring data between PC’s is awfully slow.
How I can diagnose what is a problem? What i can do to transfer data not
using usb flash drive?

Thanks

Piotrek