Panny plasma Vs Comcast HDTV, HELP

Hey folks. Need some help here

I got myself a Panasonic 42in plasma, model # TH-42PD50U
I have 2 ways i have been trying to watch the TV

Currently, i have the HD box set up passing HD through the component (comcast HD boxes DO pass 1080I through component)to the plasma. Also, i have the COAX from the HD box connected to the COAX input on the Plasma.

When watching the source through the COAX input, i am unable to get the HD (as expected). When watching standard definition programming i can use the aspect button to switch from Full, Just, 4:3, and ZOOM to find the best way to view the program. on the 4:3 there are grey bars on the sides, and the other 3 methods will stretch the pic in different ways so i can select which is the most desireable.
However, NONE of the menu's will be displayed, i cannot get the channel guide to show up through the COAX input.

When watching the source through COMPONENT, i am able to recieve 1080I signals, everything looks crisp and lush, however, on standard definition channels the picture is broadcast 4:3 aspect to the TV. This results in the black bars on the left and right side.
The TV has an ASPECT button, however, when watching through COMPONENT the ASPECT button DOES NOT WORK. The TV will not go into Zoom, Full, Just, or 4:3 mode.
When watching the HD channels it WILL go 16:9, the 4:3 HD signals will show the grey bars on the side, or some wierd moving pattern with channel logo's and stuff depending on the channel. When watching 16:9 aspect the entire screen is used and works as it should, and i should also add, it looks SPECTACULAR. The channel guide and menu's from the cable box WILL show up.
The biggest pain in the ass is that the SD WILL NOT fill the whole screen, and the ASPECT controls do not work, meaning that if i get a wide-screen movie on demand, then i have black bars on the TOP, BOTTOM, LEFT, AND RIGHT of the screen!!!

So, as a work around, when i am watching an HD channel i watch through the component, and when watching SD i watch through the coax so i can use the aspect mode to fill the screen. When searching the channel guide i have to flip back to the COMPONENT input

My buddy has a Panasonic CRT HDTV with the same box, he uses the HDMI and his TV will broadcast widescreen in widescreen, and his Aspect control WORKS with the SD. He doesent seem to have this problem.

Does anyone have this TV? Have you used it with HDMI?
Im thinking that i might need an HDMI-to-DVI cable in order to be able to use the ASPECT button with the SD in order to fill the screen.

Ugh, i hope this isnt too confusing, but it is complicated to explain.

Basically

Watching from COMPONENT
ASPECT button WILL NOT WORK, SD is broadcast with black bars, without the use of the Aspect i fear i might get burn-in.
The cable guide DOES DISPLAY

Watching from COAX
ASPECT button DOES work, HD does not, and the channel guide DOES NOT SHOW UP.

Is there any way i can have my cake and eat it too? Should i get the HDMI cable? I really dont want to blow another 100 bucks just to find out that doesent work either.

Ugh... why cant i just have 1 input that will show the cable guide, have full use of the aspect button, and get HD?

ALSO, My denon 2900 connects to the Denon 3805 via COMPONENT, then to the TV via component, the aspect does NOT work with the DVD player either.... im starting to think the aspect function will work with coax but NOT COMPONENT, maybe it will work with HDMI?