It's not easy with the PX/PV TVs.
With acknowledgement to poster autosapien - he explained it very well ...
The VGA input can accept and display the native resolution of the plasma, ie. 1024 x 768 pixels. This means when you set your PC/Mac desktop to 1024 x 768, every desktop pixel is perfectly mapped to every screen pixel and the internal scaler of the screen is disabled. The result is a razor sharp desktop and text. So whatever video content you watch, it only needs to be scaled once, eg. PAL video is scaled by the PC/Mac from 720 x 576 to 1024 x 768 and sent to the display where it is displayed at 1024 x 768.
The HDMI (or Component) input cannot accept the native resolution of the display. It can only accept SD and HD video resolutions (ie 1280 x 720, 1920 x 1080) as opposed to PC resolutions such as 1024 x 768. So if you set your desktop to one of these supported video resolutions (say 1280 x 720), the PC/Mac will scale PAL video from 720 x 576 to 1280 x 720 and send that to the display. The display's internal scaler will then rescale the 1280 x 720 to the screen's native resolution of 1024 x 768, resulting in two scaling operations.
The only option to avoid this double-scaling via the HDMI input would be to set the desktop to 720 x 576. However, many cards may not support this resolution, and of course it's not HD!
In short, the scaling operations are as follows:
PAL video via VGA = 720 x 576 -> 1024 x 768
PAL video via HDMI = 720 x 576 -> 1280 x 720 (or 1920 x 1080) -> 1024 x 768
To make matters worse - Panasonic PX/PV series TVs overscan badly on HDMI and Component - I gave up with HDMI and Component from my HTPC and just used VGA instead - relying on a single re-scaling done by my PC graphics card - not ideal!