how do i populate the body of a new post through url parameters?

Hey hobbs6487,

You should be able to do this using jQuery. Here is a post about how to use the Lithium loaded jQuery. Alternatively you can load your own jQuery.

http://lithosphere.lithium.com/t5/customer-connection/Is-JQuery-loaded-into-the-lithium-platform/m-p/17854/highlight/true#M1057

You can use the <@liaAddScript> directive in a component as you see used here:

http://lithosphere.lithium.com/t5/developers-discussion/LITHIUM-jQuery-perform-code-with-2-seconds-lag/m-p/72774/highlight/true#M2457

You can upload one or more .js files as assets through the Community Style tab in Studio if you want to keep the size of your javascript logic in the <@liaAddScript> directive small, but you'll need to pass the LITHIUM.jQuery object into all of the functions you define in your .js files (Thanks DougS ) 

Note: that there may be a lag between the page load and the filling in of the subject, and body.

I'm not sure if you can fill in attachments using this method.

Hope this helps,

Yuri