1) Simple edit control
+Very easy to implement (already)
+Very fast (in terms of using PC resources)
+Looks well with other gui controls
*/-Offers only plain text display
2) RichEdit control
+Easy to implement
+Fast
+Offers advanced text formatting (try WordPad)
+Text from (1) will still displayed
*Links are automatically highlighted (requires some additional work to process clicks on these links)
-Ugly looking (even if read-only - it display itself as ready to input edit control)
-No image support
3) Embedded IE control
+It's like IE... You can use any html file or display a web-site within it
+Text from (1) will still displayed. This means that you do no need to create complex html file for every mod. Everything that works in "big" IE - should work here
-No direct control over this control. You can post any links inside this control, point to big image files, execute JavaScript or other
-Can be bugged. Depends on IE installed in system
-May be hard to implement well
-May be slow
4) Embedded PDF control
+Better than IE
*Requires Adobe PDF reader installed in system
-No direct control over this control
-May be slow

I personally dislike every one from this, so there is a my proposition:
5) A tab control with different info on each tab
+Very fast
+High control from the program
+Will look well with other program parts
*/-Requires more coding (not hard, but not easy)

For example

On first tab should be displayed simple text: no links, no images
On second tab should be author info + some links (see image)
On third tab (i think) should be list of small screenshots. Clicking on image will enlarge it to original size or to fit window size

I will try to make a demo later