My hdtv is only 720p or 1080i it displays vga at 1360x786 perfectly but when i switch to hdmi it wont work right only in 1024x786??? wtf why and to top it off i ordered a Onkyo HT-S5300 for surround to complete my theater experience. I believe ill be able to run the sound the the hdmi only and keep video on vga but id like to be able to run it with one cable but will do it the other if necessary.
PC's display in progressive typically, mainly because monitors display in progressive too.
HDTV's have less HDMI handshaking standards than PC monitors do because the manufacturers know that the main devices connecting to the HDMI inputs will be other devices limited to 1080, 720 etc while PC monitors must accommodate for 480, 720, 768, 900, 1050, 1080 right up to it's native resolution.
So when you connect your PC to your HDTV, the HDTV will display at the best resolution it is capable of, 768P, since the PC will not like 1080i as it is not a standard the PC is used to.
The VGA connection may support better handshaking methods as it is usually a dedicated PC connection, which may explain the better resolution.
If you have an Amp to run the HDMI connection through firstly, see if it will upscale to 1080i for your TV.