I've edited your post a little, I hope you don't mind. I want to first mention we don't condone in anyway copyright infringement.
Downloading speed is determined by a number of variables. The first thing you want to do is make sure the ports in your router or firewall are open that the P2P client uses, there will be many guides on how to do this on the P2P clients website. Also, and most importantly, the number of seeds and how fast they can upload. You often find on private torrent sites, because it's in the benefit of the seeders to seed, you can much faster downloading speeds for files that you want.
As for the quality of the video file, it is determined again by a number of variables, the key ones being: bit rate, codec and resolution.
The typical American resolution size is 640 by 480 for a 4:3 file and 720 x 480 for a 16:9 file (T.V widescreen). PAL television on the other hand, always works at the resolution of 720 x 576 and is stretched to the appropriate aspect ratio. These are the resolutions you find typical files in.
Bitrate determines the quality for a particular codec, the higher the bitrate, usually the higher the quality. However the type of codec is more important than the bitrate if there's only a spall difference, in order of popular codecs here is the quality from bottom to top:
mpeg2 < divx < xvid < vc-1 < h264
vc-1 is also known as wmv-hd, it's part of the wmv profile, but significantly better quality than the old wmv codecs. So for example, a 350mb 45min h264 file, if encoded properly, will look tonnes better than a 350mb 45min mpeg2 file.
When practically finding stuff, the mainly level of qualitys are often determined by resolution. So a standard file will be 350mb xvid 45 mins, you then get high resolution files often tacked with HR on the end, these are scaled down HD files, they're slightly higher quality and slightly higher resolution at 650 - 700mb xvid 45 mins. Then you get high definition files, the first lot is 720p, which is a resolution of 1280 x 720, these files are almost always encoded in h264 and you need a new CPU to play them (AMD64 line ore Core2 line are all very likely to play them with the right Codec, CoreAVC is the best CPU saving device for h264 files). A typical 720p file is either 1.1GB or 1.44GB for 45 mins. 1080p and 1080i aren't quite as popular yet, but you can get hold of them and they are a resolution of 1920 x 1080.