It'll be up Monday, probably. It's nice to see it used. I'll replace it with a png-zip as you suggested. Also, somebody over at the UT3 modding forum I put this on asked for a skybox tutorial, so her it is, if you're intersted. If you're not, feel free to ignore it.

BEGIN LONG TUTORIAL SEGMENT

1. Create a sky in Terragen. This tutorial is for Terragen 1, but Terragen 2 should be usable if you want to figure it out. [Link] This is art. It's not a hard program to learn to use, but it's not easy either. There are no end of good tutorials for it, I used some of them and taught myself a lot. I can't explain exactly how to do it here.
2. Set the image size to 960 by 960. This is the largest square that the non-licensed version will let you render. Make sure you have the land turned off, obviously.
3. Save this as [link].
]------------[
initanim "C:\skyrender", 1

;_ft
Zoom 1.0
CamH 0
CamP 0
CamB 0
frend

;_lf
Zoom 1.0
CamH 90
CamP 0
CamB 0
frend

;_up
Zoom 1.0
CamH 270
CamP 90
CamB 0
frend

;_bk
Zoom 1.0
CamH 180
CamP 0
CamB 0
frend

;_rt
Zoom 1.0
CamH 270
CamP 0
CamB 0
frend

;_dn
Zoom 1.0
CamH 270
CamP -90
CamB 0
frend
]------------[
4. In terragen, go to Terragen (in the filemenu bar) and Execute Script. Choose this script and wait. 3D skies can take a long time to render. When it's done, you should have six numbered images in your root drive, whatever that is. (It's almost certainly C:\. If it's not, you can probably find it.) Move these images somewhere useful.
5. Resize these images to 1024 by 1024. It comes out a bit cleaner. You can ignore the all-black one.
6. At this point, I'll just point you to the tutorial I'm following. I can't possibly explain this better than this bloke does. [Link]
7. I have a couple of tips for anyone following this tutorial.
-ATI Cubemapgen seems not to generate it's highest-res image if "generate mipchain" isn't checked. Just delete all of the extra mipmaps.
-Put in the Y+ (top) face first, so that you can instantly tell if they are lined up.
-Check the 'skybox' box to get a better idea of what it looks like.
- I believe the face orders are as follows:
X+=skyrender0004
X-=skyrender0001
Y+=skyrender0003
Y-=skyrender0006
Z+=skyrender0005
Z-=skyrender0002
- I'm using a 1 pixel clone brush from a pixel within one or two of the line at 800% zoom to remove the black arcs from the panoramization.
8. If you want to do any manual editing of this image, I would check out Panotools PEditor. [Link] It's a bit awkward, but it's better than nothing. Do any editing with this program BEFORE you crop your image, otherwise all hell will break loose. PEditor likes full-dome panoramas UnrealED likes half-domes. Of course, you could always add a lower half that's all black just to edit it in PEditor, then crop it again...