Deployment Solution

I have installed DS 7.1 onto a server with IP 10.0.x.x. This is on a VLAN for servers. DHCP is enabled on a server with IP 172.16.x.x (different VLAN) and a scope configured (10.1.x) to service endpoint devices on yet another VLAN. Endpoints successfully obtain a valid IP via DHCP when booted into Windows courtesy of a helper address on the switch/router. The DS can ping the DHCP server and the endpoint once it has booted to Windows.
What needs to be done to allow the endpoint devices to PXE boot to the DS server? 

TIA

Mark

Some basic stuff to check

There are several steps to get DS 7.1 up and running:

- Step one is start the PXE services (default start is set to manual, see https://kb.altiris.com/article.asp?article=52235&p=1)
- you need to create and enable a boot configuration and replicate it to your Site Server (if you don't have a Site Server, make the NS a Site Server)
- for existing clients you have to create a task to boot them into WinPE before you can assign an image job and you have to assign another to boot back into production after your image is done or the machine will loop into PXE
- for new clients / bare metal deployment you have to check checkbox to respond to unknown computers

there are a couple of good KBAs in the knowledgebase (kb.altiris.com) and I'm sure you can find more information on connect.
there are some KBAs on using IP-helper and forced mode for PXE, too, they might come in handy for your setup.

PS: If your server has multiple NICs in different subnets/VLANS, yo need to make sure DS used the right for the PXE service

I'm ok with getting the PXE services working and creating PXE boot configurations on the NS - it's as slow as hell, but don't get me started on that. Ok, you have. In the good old days of DS 6.x any changes made were, as near as makes no odds, immediate. In 7.1 if one lets things just happen changes to PXE boot menus, initial deployment options, PXE boot options, etc can take ages (determined by the agent's 'phone home' period and some don't happen until the PXE services are restarted (or so it seems). Too put it mildly, it's a little frustrating.

Got the VLAN issue sorted using IP helpers and forced mode. Some useful links:
PXE modes of operation https://kb.altiris.com/article.asp?article=27249&p=1 The DHCP server needs a  few options adding including Option 43 that requires an entry in hex. Not as bad as the document makes out

DS7.1: How do I set up PXE services on a Deployment 7.1 server? https://kb.altiris.com/article.asp?article=51467&p=1