Rendering is related to a lot of of hardware. If I understood, you said that your MPEG2 rendering are only 3 minutes of video per hour? There are very wrong things happening. First of all, what is your machine?
In my home P4HT 3.0 with only 1GB DR2 533 Kingston, 128 mb Geforce 400 and Sata HDs, [B]without[/B] a video capture card, full NTSC DV rendering with watermark logo applied all long of the timeline and 12 secs crawling text repeated four times, the rendering is 1 minute of video per 3 minutes (1:3) of rendering. Without crawl and watermark, things are almost 1:1,2 relation. And this, in a machine connected to the web, running Firefox, AVG, Zone alarm, Spybot... You are reporting a 1:20 relation...
If you have a capture card, some rendering is made by it's processor. Slow DDR1 memories means very slow renderings. Slow one core CPUs means slow rendering. Slow IDE HDs means slow rendering. Windows XP fast search archiving, and restore point creation activated, means very slow rendering. Fragmented HD means slow rendering. UDMA settings of HD have to be working.
Some virus and trojan may slow your computer. Anti-spyware slow things down.
CPU connection and cooling is a factor too. CPUs with pins are slower than contact CPUs. Mainboards are a factor too. Intel are faster an Asus, that are faster that PCchips, that are faster than others. Cooling is so important that actual Intel Quadra Core mainboards have cooling at all outputs of the board. Really creepy. Lack of "hot paste" between CPU and it's cooler my kill your speed.
Gold plated memory and slots contacts (usually at Intel mainboards) are really faster than other metal connectors.
But the worst thing that you can do is to have [B] Norton or McFee[/B] anti-"computer" software of suites running. This is dead blow in all of your performance. They are a "brake" not a solution.
The ideal for a video edition setup is that your computer is running with less things possible in memory, not connected to the web, to not need anti-virus, anti-spyware and firewall - memory and CPU/memory hard consumers.
Today, a good 512MB video card with DDR3 accelerates the things. Memories have to be fastest as possible: DDR2 800 or DDR3 more faster. But remember that XP works only with 2GB maximum. To use 4 or 8 GB (very cheap investment today) you need Vista.
So, don't blame Vegas or Avid: look at your hardware and other software. Vegas may be used in slow machines like old Durons, Celerons. K7 and K6, while Avid needs more punch.
Avid is great because, till now is the only that have "background rendering" while you are working. My professional edition computer, at work, has it and the Quadra Core Intel really rocketed the software. But for the people who lack information and buy Adobe Premiere any version, there is nothing to do... They are dead and waiting for rendering while we are doing other things after finished the job.