How can I start a Class Action Suit against Qwest for overcharging customers on "high speed" DSL?

This is a quest probably better placed in a legal forum. That said, you will first need proof that they are overcharging, and doing so with the express knowledge that they are "over"charging.

If you can prove that, you can start talking to a lawyer who can help you get the process moving.

However, you will be hard pressed to prove that they are overcharging. They will legitimately be able to respond by saying that the pricing is set by market conditions, and that the price is competitive. Price gouging is very hard to prove or convict on, especially on non-essential services.

You need a lawyer, willing co-plaintiffs, and media coverage for a successful Class Action Suit.

I thought their prices were getting rather high...but I think the first step would be to speak with a lawyer.

i don't think, because in the contract you signed it stipulates that the service rate can change without the customer approval and previous warning of it.

You need a lawyer for that.