My understanding is that you would like to use your Fedora Core 3 DHCP server to hand out IP Addresses to all of your 3 VLANs;
If this is true, then there are 2 different ways I can think of:
1) Trunk link to your Linux network card using 802.1q tagging.
This requires you to setup a trunk link between your main switch and Linux DHCP server. Assuming your switch supports VLANs (and therefore Trunk and Access links), Linux fully supports trunking, so you've covered.
2) Install 3 network cards on your Linux system, configuring one card to each vlan and connecting them via an Access link to your switch. Each port of your switch will need to be assigned to one vlan.
I love this site! When I originally read the first post in this thread and Chris' response I did not have a clue about what was going on. However after following
one it all makes sense now. Thanks jwj for resurrecting the thread and making me realise this.