I use Chicken of the VNC to access my other computers over my home network, and it works great except that the mouse pointer shows up as this pseudo-fat dot instead of an arrow or whatever. I found the fat dot a little hard to see sometimes, so I looked inside the COTvnc application (control-click on the application, choose Show Package Contents, navigate into Contents -> Resources). Sure enough, there were three TIFFs representing the three pointers COTvnc uses (I have no idea what the other two are for, but sometimes they show up).
To change the pointer, just open the TIFFs (called rfbCursor.tiff, rfbCursor2.tiff, and rfbCursor3.tiff) in your favourite image editor (like Photoshop Elements), and replace them with your own 16x16 TIFF images. In Photoshop Elements you have to select a checkbox in the "Save as" dialog to make it include the transparent background. Also, you will not be able to save directly into the COTvnc app. You have to save it to the desktop (or wherever) and then copy it into COTvnc afterwards.
My renditions (boring as they are) can be downloaded, if you'd like to save some time.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040827145528277