Ok I feel like a complete idiot for asking this but.... I have not worked with maps other than indoor maps really so.......

How do you define the alpha channel for like grass to dirt in guerrilla?

Wow I feel like an idiot. :(
Wait... I am an idiot!

Don't be so hard on yourself, alpha channels can be tricky at first. If you search on halomaps there's a really great tutorial on making ground bitmaps. It's by Kirk if I remember correctly.

Elefant care to go through the process on how to make them work, I too have not been able to setup alphas properly in HaloCE.

Basically, to get them to work in CE, compile the texture into a bitmap through tool. Open it up in guerrilla. Go to format, hit the drop down box, and click Explicit Alpha. Compile the same bitmap through tool again, and the alpha will be compiled. In the shader, you can now set two different detail maps, and one will go where the alpha is in the bitmap. It will also fade out to each detail bitmap, which gives a nice effect.

I smell progress slash!