In the transport module on the toolbar, X3b is saying all of my projects are 44.1/16 bit, even though the bit depth in the audio driver settings is 24 bit. (I don't even have the option of recording at anything other than 24 bit, the dropdown menu is inactivated.) My card is an EMU 1820 that I've had forever. The bit depth is shown correctly when I use X2. Has anyone else seen this problem?

That's the bit depth used to communicate with your soundcard, not the actual audio bit depth. Check the help files for a more detailed explanation

To fix this, go to Preferences > Files > Audio Data >  File Bit Depth. Set record bit depth to 24. Render Bit depth should be 32 if you don't have performances issues and 24 if you do.

Thank you guys. I did look in the help files, but had a hard time finding the right setting. Very appreciated!

Also make sure that your sound card is not being used by windows for windows sounds as that are all 16 bit and will switch your sound card to 16bit without necessarily showing, while Sonar still seems set to 24 bit.

I had the same kind of problems with sample rates. Project was 44k and I wanted it to be 48k
 
I had to recreate projects and import bounced tracks since changing samplerate was not working.

Once your project is created at a particular sample rate, I believe it stays at that rate no matter what you do. Files imported can be converted to the rate or can be converted on playback, but mixing will happen at that rate. Also, Synth Sounds and loops etc will be converted to the project sample rate at time of playback. There has been talk about how much CPU consumption this might add on the forum.
 
I use 44.1 and 48 sample rates primarily and have never noticed latency related to synths and loops that was perceivable.
 
http://www.cakewalk.com/Documentation/default.aspx?Doc=SONAR%20X3&Lang=EN&Req=Dialogs2.052.html
 

Cakewalk Help
Sampling Rate. The Sampling Rate list allows you to enter or select an audio sampling rate for a new project. After audio has been added to the project—either by recording audio or by using the File > Import > Audio command—you can no longer change the sampling rate for that project. Therefore, you should choose the sampling rate immediately after choosing File > New to start a new song.