DHCP Relay issue

Hi all,

I am currently trying to get an intermediate solution in on my home network.
Currently we have three separate DSL lines all with their own physically separate LANs.
I am looking to get in a managed switch to implement VLANs and drop the two other DSL lines however as an interim solution I need to get some limited communication going between two of the LANs. I have routing working OK, but I'm having issues with DHCP relay.

Here's the issue.
Clients that I need to get DHCP are 192.168.10.0/24
There are also DHCP clients on the other lan on 10.0.0.0/8 although I have 10.0.1.x as the DHCP address pool for that scope.
I have added an additional scope for 192.168.10.0 but am having problems in that the clients on that LAN are picking up leases from the 10.0.0.0 scope.

10.0.0.0 LAN:
10.0.0.5 = Windows Server 2003 - DHCP server
10.0.0.140 = DSL router - Netgear ProSafe DGFV338
Routing configured for 10.0.0.0/8 to 192.168.10.0/24

192.168.10.0 LAN:
192.168.0.1 = DSL router - Speedtouch 570
192.168 0.2 = static IP assigned to client manually at present
Routing configured for 10.0.0.0/16 and 10.0.4.0/16 and 10.0.6.0/16 as I want these clients to only have access to certain areas of the 10.0.0.0/8 LAN.

DHCP Relay configured on the Speedtouch 570 to 10.0.0.5 via the eth0 interface.
I can only specify either the Interface (eth0 or ISP) or the giaddr - not both
When I try to specify a giaddr of 192.168.10.1 or 192.168.10.0 I get the error "IP Address not found in DHCP server list"

Can anyone help on this? If it's impossible or very tricky, I'm not too worried and can stick with manual IP assignment as it's only a temporary solution until I get my managed switch and VLANs in place.