How do I export an InDesign file (CS2) to be an RGB PDF?

As a last resort, you can convert the entire document to an RGB color space using Acrobat (as long as you have Acrobat Professional, not Reader.)

Open the document in Acrobat, then go to Advanced > Print Production > Convert Colors. In the top section of the dialog, choose "Device RGB: Convert." In the Destination Space section, choose: Adobe RGB  (1998).

There is a lot more going on in this dialog box. For a full explanation, check out the Acrobat help page: http://help.adobe.com/en_US/Acrobat/9.0/Professional/WS58a04a822e3e50102bd615109794195ff-7b96.w.html

Thanks, Casinnola.  I tried this and it didn't work.  To answer your question, Sheharyaar, I've tried several different "RGB" in the Destination dropdown box, such as ROMM-RGB, sRGB,  and Adobe RGB (1998) and this didn't work either.

It looks like my issue is that actual source InDesign file.  Some pages are in RGB and some pages are in CMYK, and I don't know why.  The exact same image shows up on some pages as RGB and some pages as CYMK.  (i.e., I'm using the same image as a header and frame throughout the book, and it is not showing up consistently).  I can't figure out why.  Any other thoughts?

so you are saying, you already have RGB images which you are using in the indesign document
but when you are exporting the PDF, some pages are coming as CMYK?

Try this:

1. From InDesign, click File > Print.  
2. For Printer, choose "Adobe PDF."  
3. In the left side of the Print dialog box, click "Output," then under the Color dropdown menu, choose "Separations."  
4. Now click Print and choose a location to save the resulting PDF.  
5. Once your PDF is finished, go through it page by page. It will be a little confusing if you've never looked at separations before. Each "page" of this PDF will have black text or images on it. It's showing you what a plate of for that page would look like. But here is what you're looking for: in the "page number" field at the top of your PDF, you will see something like this: the first page might be called "Black:1", then the second page is "Red:1", then "Blue:1", etc. The color is telling you that this color swatch was used on that page, and the number after the colon is the actual page number (as it is listed on the InDesign file.) So depending on the number of different swatches used on each page of your InDesign file, this Separations PDF might be pretty long. But what you have to find is a page in your PDF that is using a CMYK swatch. Once you've located a page in your PDF that uses a CMYK swatch, look at everything that is displaying on that page. These are your culprits.  
6. Once you have identified where the CMYK color is, you will have to replace that CMYK swatch with an RGB swatch. 

Now.... there are easier ways to look at Separations in an InDesign document. But it's been 3 years since I've used CS2 and I can't remember what options you do or don't have. I know that this Separations PDF will work for you, that's why I'm suggesting it.

Thanks Casinnola - I had never looked at color separations before and you were right, this worked!
It does show me the culprit -- but I still have no idea why the EXACT same image appears in RGB on some pages in the the InDesign file and in CMYK on some other pages.  Do you know why that would happen - where I could copy and paste an RGB image onto another page in the InDesign file, and it would show up as CMYK? I'm stumped as to why it happened!

I'm just going out on a limb here...

Go into your links panel (Window > Links) and look at the entries for the images in question. You say they're the exact same image... make certain that each instance of that image is, in fact, linked  to the exact same file (and not different copies of the same image.)

not sure why there's the insistence to make sure all pics are RGB, wouldn't matter if there were some CMYK for screen... its when its going to PRINT that all pics are meant to be CMYK (parking more recent RGB workflows for a second here)

nevertheless, go file, adobe pdf presets, then smallest file size. in the output tab, make sure that convert to destination is selected, that an RGB profile is selected (doesn't matter which one unless you have a preference) and don't include profiles. that's the key... all the other guff (whether to downsample images or not) is up to you to change.

i've tested this theory on a black-text only job and in my seps panel in acrobat, the black showed up in RGB but NOT the non-device CMYK, where it should've normally.