If you look at the backplane (3rd photo) you'll notice two blanking slots.
These are for full sized PCI slots on the riser board.
Previous post is correct that the white PCI slot next to the AGP 4x slot
is indeed half height.
But the other two are not.
For example I have a Full Size PCI Winfast T1000S card in one of my slots
and a full sized PCI StarTech 4x USB out on mine.
For me, I am still on XP SP3 (not sure I want to run Windows 7 ... I still have nightmares about Vista!).
I did however have major snags getting widescreen of the latest XP DELL drivers for the GX260.
So if you have the money, I would recommend getting a dedicated PCI card.
AGPx4 cards are like gold-dust.
I am told that you cannot put a AGPx8 into a x4 slot (ie unlike memory that will chose the slowest common speed I am told AGP wont do this).
Of course, since I have never tried this I dont know how good that advice is. But the PCI cards do work well.
Also, I only have a P4 2.0GHz processor and it struggles.
I am not RAM bound (1.5 GB on XP is fine, Vista wouldnt cope with that
not sure about Windows 7).
Having said that, if the PCI graphics card supports Direct X to the correct level for Windows 7, maybe it can take some of the workload of the CPU.
You say you want to do HMDI 1080p (I think you do ... your pictures are HD res).
So since this involves lots of mp4 decoding via H264 codec (which normally you have to buy from somewhere) AND the software versions wont necessarily use the GPU, I guess you need to do some serious research.
To be blunt, wouldnt it be cheaper (in long run) to buy a new machine and take a shotgun to the GX?
My wife uses ours for word proc/admin/email/browsing and we deliberately kept it on XP (which was a lot faster than Windows 2000).
This type of DELL was not designed with Windows 7 in mind.
A nice new machine will have PCI express, and a cheap one will have nVidia inbuilt into the motherboard.
My barebones system (150GBP for 2Gb, dual core core duo system, disk drive/OS/monitor extra) runs HDTV really fine!
Indeed, I put the TV card into the DELL and got a satellite card (that can receive HD signals) for my box.
That's when I had fun finding H264 codec and noted that some will use the GPU, others wont.
There is no way on this earth that a single core P4 could hand HD without GPU support ... well not unless it was seriously overclocked.
Good luck with your quest.
Regards
Steve H