All the current plug-ins for Windows, both 32-bit and 64-bit work with CS5.
You can move your plug-ins over to CS5 by going to: C: \ Program Files \ Adobe \ Photoshop CS4 \ Plug-ins and copy the Topaz files and put them in C: \ Program Files \ Adobe \ Photoshop CS5 \Plug-in
64-bit users have this file here: C:\ Program Files (x86) \ Adobe \ Photoshop CS4 \ Plug-ins
MAC:
Complete 64-bit CS5 compatibility for Mac is now available. These new versions are free to existing customers. To download and install the update, simply re-download the software you own from the Topaz downloads page re-install it on your computer. After re-installation, the Topaz plug-ins will appear in the Photoshop Filters menu.
If you previously had Photoshop running in 32-bit mode don't forget to change it back to 64-bit mode. To do this go to HD -> Applications -> Adobe Photoshop CS5 (folder) and then inside of that folder right-click (control-click) on the actual Adobe Photoshop CS5 application and select "Get Info". Under the General section, uncheck the box next to "Open in 32-bit mode". After that, restart Photoshop and you will be back in 64-bit mode.
If you have done the steps above and Topaz is still not showing up in your Filter menu under 64-bit Photoshop then you may have some old files left over causing a conflict. So please do the following:
1. Go to Macintosh HD -> Library -> Application Support -> Topaz Labs and remove the existing plugin file (using Adjust as an example, the plugin file, Topaz_adjust4.plugin, is inside Topaz Labs -> Adjust 4 -> Plugins. (You will need to enter your system password to OK this change).
2. Delete any previous Topaz download files from your computer
3. Clear your temporary internet files (Cache)
4. Download and install the program(s) again. Make sure that Photoshop is closed while you are installing.
After that, open an image in Photoshop and then you should be able to access Topaz from your Filter menu