You can find a lot of details at HP's website just by searching on key info. Should be a first stop for any searches.
I checked the specs at
Motherboard Name: H-I41-uATX
HP/Compaq motherboard name: Evans-GL6
You can find the H-I41-uATX motherboard detailed information at:
Also, the system specs state:
As noted in Meats_Of_Evil's earlier post, power could be a major factor. 220W is a VERY low total wattage power supply. Total +12V watts capacity is likely marginal.
The motherboard specs stipulate:
Motherboard Form factor
micro-ATX: 9.6 in X 9.6 in
so, if you get a case that supports that form-factor you should be able to do things like beef-up the PSU.
The motherboard specs page also includes a layout diagram and photo of the motherboard.
The system specs for the expansion slots simply say:
PCI Express x16..........................One (One available)
PCI Express x1.............................One (One available)
PCI Express x1 minicard socket...One (One available)
No reference to 1/2 height/mini restrictions for the PCI-e slot.
Nor explicitly which PCI-e version is supported, but one might
assume 2.x An older PCI-e version would restrict what video cards you can use. And of course we still don't know what form-factor would fit internally due to adjacent components or other adapters. The specs are pretty light on details.
And, if you're planning on dual-display capability by using the integrated graphics and a graphics card, that isn't supported.
"Either integrated graphics or the PCI Express x16 slot are usable at one time; they are not usable concurrently."
edit to add:
After looking at the layout of the motherboard, I'd say the ability to support a number of graphics cards is probably limited because of possible obstruction from adjacent components, even if put into a larger case. But, it is hard to tell for sure from just a single perspective view.
edit: minor clean-up