Hi Marty,
The answer is YES, it's gonna be fine. I've got a HP Pavilion desktop that has the "older" version of the same motherboard and I've got a GTX750 installed - it works perfectly. My board is the MS-7613 (Iona-GL8E) your one is an MS-7906. I compared their specs and they are 90% identical. As with my one, your card will go into that long black Gen3 PCI Express x16 slot.
And regarding the PSU; that shouldn't be a problem either. I've got a 400W PSU. This card's power usage is only 55W which is mindblowing for what it does.
When I was looking for a video card replacement the rich gamer kids on the forums (or kids with rich parents) kept saying "don't buy anything 'below' a GTX660" but I don't have the money for a $600 card so I went with the GTX750. More specifically the EVGA GTX 750 SuperClocked (
http://www.pbtech.co.nz/index.php?z=p&p=VGAEVG2753) because EVGA did a great job with overclocking it (so that I don't have to) and it had the perfect outputs for my screen setup. I fly FSX DX10 with an average of 55-60 FPS (however, bare in mind that I fly bush so no PMDG, and no monster airports). My only mistake was that I bought the 1GB one. It's not a showstopper, but some games out there really need a 2GB card. That's not a problem for me as I don't have time for games - I happy if I can fly once a week nowadays
Anyways, I think it's a good buy, and it won't disappoint you.
Dan
PS - Don't let this single support issue put you off HP. They're pretty good when it comes to desktops. And let's be honest - have we seen any big brands that has proper support/communication? They don't car anymore. I've had no issues with my HP Pavilion for 6 years now. The only thing that I had to do was replacing that tiny motherboard battery (which is quiet normal) and blow the dust out of it every 3 months. I also think they do a good job with balancing their desktops. I know, I know...The best PC is the one you build yourself. And I could do it, but again, I don't have the time....