well if you don't know css, you should consider learning it sometime. It's not that complicated, I could actually code with it within the hour and just took me a few more hours to get the hang of it and code my layout.
If you do not have any of these programs except for Nvu and gimp, I would suggest you start manually coding it (maybe in tables since you don't know css).
Just make the layout with gimp, make the header with gimp aswell... (keep in mind you need the right sizes/proportions). As for the rest of the site, try and just use tables and color to make it look nice. The best layouts are those that are simple, fast loading, and very easy to use. No sense making a very complex layout if it's hard to navigate. If you wanted the content box to be rounded at the edges, use either css or create the rounded edges with gimp and then insert as background into that cell (not the best method but if you don't know css it's one of the few ways to do it).
Also if you need something sliced with photoshop, I'll be glad to do it for a few NP$.