Loosing spaces with AJAX POST

I'm just implementing the FCKeditor for the first time - nice work! ... but I'm having trouble with my AJAX and I wondered if it was an FCKeditor related problem....

I initially used the the GET method for my xmlHttp.open but I soon discovered this would limit my input in the editor to a tiny 512bytes of text. So I switched to POST

Here's the code:

theEditor=FCKeditorAPI.GetInstance("SJSEditor"); 
xmlHttp.onreadystatechange=stateChanged;
         xmlHttp.open("POST",url,true);
         xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded; charset=utf-8");
         xmlHttp.send("q="+theEditor.GetXHTML());

The trouble is, when I send the data I loose all the spaces in my input.

I am POSTing the data to an ASP page, retrieving it with Request.Form("q") and then sticking it in a database.

I figured it was something to do with the 'urlencoding' which replaces spaces with +s, so I thought I could escape before passing the data like this:

xmlHttp.send("q="+[b]escape[/b](theEditor.GetXHTML()))

Great! This worked. My spaces are returned. However, a new problem:
I can't enter any ascii characters as FCKeditor converts these for me, and then escape converts them again so £ becomes £ and then £ - Obviously this is no use.

So now I am back to trying to discover why I loose all my spaces as it seems better to let FCKeditor do its thing and then fix it rather than trying to second guess!

Any help much appreciated.