As others have stated: Have a new job lined up before submitting this letter. Make the letter neutral, and keep the frustrations to yourself.
You may be able to use your current employment as leverage as you locate this new job. I was personally in a very similar situation, the end result was that the new company wanted to hire me ASAP and offered a decent pay raise over my current job; I put in my two weeks notice and revealed nothing. In the end, I was offered a raise at my old job (turned down); months later they wanted to contract me for some work on the weekend, and they've made it clear there's an open door if I ever want to return. Requesting two weeks before you can begin work (for time to put in your two weeks notice) to your new employer also demonstrates your loyalty and stability, something a good employer will recognize & respect.
edit: My resignation also marked the first of my team's mass exodus. 6 months later, everyone I worked with has left, and they've got a completely new team. A word of warning (at least in the US), you don't want to be caught trying to get your coworkers to leave, and especially not to get them to follow you to a new employer.
You may be able to use your current employment as leverage as you locate this new job. I was personally in a very similar situation, the end result was that the new company wanted to hire me ASAP and offered a decent pay raise over my current job; I put in my two weeks notice and revealed nothing. In the end, I was offered a raise at my old job (turned down); months later they wanted to contract me for some work on the weekend, and they've made it clear there's an open door if I ever want to return. Requesting two weeks before you can begin work (for time to put in your two weeks notice) to your new employer also demonstrates your loyalty and stability, something a good employer will recognize & respect.
edit: My resignation also marked the first of my team's mass exodus. 6 months later, everyone I worked with has left, and they've got a completely new team. A word of warning (at least in the US), you don't want to be caught trying to get your coworkers to leave, and especially not to get them to follow you to a new employer.