iDVD has a 99 chapter (or as in this case, slide) limitation.
There are many ways to produce slide shows using iPhoto, iMovie or iDVD and some limit the number of photos you can use (iDVD has a 99 chapter (slide) limitation).
If what you want is what I want, namely to be able to use high resolution photos (even 300 dpi tiff files), to pan and zoom individual photos, use a variety of transitions, to add and edit music or commentary, place text exactly where you want it, and to end up with a DVD that looks good on both your Mac and a TV - in other words end up with and end result that does not look like an old fashioned slide show from a projector - you may be interested in how I do it. You don't have to do it my way, but the following may be food for thought!
Firstly you need proper software to assemble the photos, decide on the duration of each, the transitions you want to use, and how to pan and zoom individual photos where required, and add proper titles. For this I use Photo to Movie. You can read about what it can do on their website:
(Other users here use the alternative FotoMagico: http://www.boinx.com/fotomagico/homevspro/ which you may prefer - I have no experience with it.)
Neither of these are freeware, but are worth the investment if you are going to do a lot of slide shows. Read about them in detail, then decide which one you feel is best suited to your needs.
Once you have timed and arranged and manipulated the photos to your liking in Photo to Movie, it exports the file to iMovie as a DV stream. You can add music in Photo to Movie, but I prefer doing this in iMovie where it is easier to edit. You can now further edit the slide show in iMovie just as you would a movie, including adding other video clips, then send it to iDVD 7, or Toast, for burning.
You will be pleasantly surprised at how professional the results can be!
To simply create a slide show in iDVD 7 onwards from images in iPhoto or stored in other places on your hard disk or a connected server, look here:
How long is your slideshow? iDVD can do one hour on a single layer DVD and about 2 hours on a double layer DVD.
I have done a 300 photo slideshow in iMovie that worked fine, but it was only about five minutes. There is no limit on the number of slides iDVD can handle as long as they are part of a single movie.
The slide show is not very long at all, at the moment it is about 200 (less than 30 mins) slides plus tranistions, I am not sure why it is so big? I import the files into iPhoto as an event, then then transfer them to iMovie, drop them in then adjust the slide length and relvant transitions, 'share' the project into iDVD, it does everything it is meant to but when I burn it to disc it wont work as the file sizes are about 7.5 GB (to big for a standard single layer 4.7 GB disc?).
What is going on? lol
When you share to iDVD, try this...
In iMovie, use SHARE/MEDIA BROWSER/LARGE
In iDVD, Go to the Media Button, then look for Movies, then find this movie (that is the Media Browser copy.
Get the large size if you have saved in multiple sizes.
If this is what you have already tried, I am out of ideas.