Problem with DHCP through WLAN AP

Hi Folks,

I have the following (now already annoying problem) with my network
configuration.
The situations looks as follows.
1.) I use a Linux (SuSE 9.1) Server with dhcpd, BIND, firewall etc. installed as main server for my mixed network consisting of XP Pro and Linux clients
2.) I use an access point (WG602v2) for WLAN access to my network which its IP configured through one entry in the dhcpd.conf file on the server.

So far so good. Now I bought a new gadget named Sirocco Wireless Audio
Bridge which operates via WLAN (ethernet also possible but I have to use
wireless because of cabling constraints).
The problem is now as follows. When I connect the Sirocco wia CAT-5
cable to the network everything is fine and the device gets an (via MAC
identified IP-address from the DHCP server). When I do not use the cable
but want to connect via the WLAN AP the device gets not recognized by
the DHCP server!

I'm arguing that the DHCP packets do not get through the WLAP AP
(however my WLAN equipped notebooks do work with DHCP) or the
problem is related to the Sirocco itself (it is not possible to set an fixed
IP at the Audio bridge which is not very flexibel though).

Any Ideas?

Thanks for the help.