My HDTV does not have HDMI input, only PBY and RGB. Will I lose video quality when plying a HD movie?

No. Component cables work well with HD video even up to 1080p. It is a trivial challenge using standard def DVD's.

The one issue is your TV will do a Analog->Digital conversion if you feed it component signals. Depending on the TV, this might create an artifact or two.

But I have to use component cables for my BluRay player (it wont play well with my HDMI switch), but I found no difference in image quality between the 2 connections.

Well, technically yes. HDMI is said to produce better video quality than component cables. However, both will give you 1080i/p video output and you likely wont notice the difference. It definitely shouldnt effect regular DVDs as those are standard definition.

yes to some degree. it also depends on the size of your tv and the quality of it. 1080p really benefits the larger tv's 50 inches and up anything smaller 1080i,720p etc will work just fine. the hdmi cable is the best connection available. other connections can produce good qualitly images on smaller screens but for larger screens, again, hdmi is better.