As you know, OpenOffice doesn't come with the dazzling depth or array of templates that Microsoft Office users get. However, here's the thing.
A) Templates aren't software. You can get great free software, without many templates, then go out and get the templates separately, also for free.
B) You can use Microsoft Office format templates to your heart's content in OpenOffice.
So here's what I just did.
1. Googled free Microsoft Office templates.
2. Picked this of the many results. http://www.presentationmagazine.com/free_powerpoint_template.htm
3. Downloaded this one (a dear friend just got married to the man I set her up with -- it seems an appropriate choice. :) ) http://www.presentationmagazine.com/wedding_powerpoint_template.htm
4. From OpenOffice, chose File > Open and opened the downloaded file.
5. Now, I can just use it, save it as a presentation, do whatever I want at this point. However, if I want it in that nice little catalog of templates that pops up when I create a new presentation....
I choose File > Templates > Save and name it, then click OK.
6. And now (without restarting or anything) when I choose in OpenOffice File > New > Presentation, that wedding template is right there in My Templates.