Broadcasting from an NDIS Intermediate network driver

Hi,

I have an NDIS intermediate network driver which I'd like to periodically broadcast a UDP packet from. I have put an NDIS_MINIPORT_TIMER in my miniport's initialize function and this is now triggering a routine every 100ms. In this routine I do the following:

NdisAllocatePacket
NdisAllocateBuffer
NdisChainBufferAtFront (to chain the packet above to the buffer above)

I am a bit confused as to where I can put my payload, is the buffer that is allocated the start of my payload, so can I start building it up in there, or do I need to create an ethernet frame, then IP, then UDP?

I've been looking at send.c in the ndisprot example DDK code but it's just confusing me further.

All I want to do at the moment is have my timer routine broadcast a small UDP packet when it is triggered. Does anyone have any pointers or example code I could look at?

Thanks

Richard