Using the image_rotator plugin will invalidate XHTML because it gives all of the rotating images the same ID.
Alby: There you go

In attach there is a testing version 1.7
- Add images_only param (overwrite search image files and use this images only in same order). It's comma separated of filename image. Example: images_only="1.jpg,2.jpg,3.jpg"
- Add background (rotator=new only) param with a rotator_placeholder div. It's RGB hex code. Example: #ff0000
- Bugfix for avoid XHTML validation (rotator=new only)
Please test this tag. Rename file to .zip
EDIT: there is a 1.7b that with insensitive caseAlby