A "VA" or "volt-amp" is a watt. Sort of. You need one that will support all of that hardware. Your PC's power supply is liable to be 350W by itself, and the CRT is liable to be pretty high wattage, too. Add them up and make sure you get something that will support all that power. Now, if you get something that's going to support 5W more than your consumption, you're only going to have a few minutes worth of uptime. If you just want to live through a bllip or allow everything to shut down properly, then that should be okay. But if you want to weather a longer outage, you'll need something with more capacity.

APC has a UPS selector that might help you size the correct UPS for you.

If you just want to weather a blip and shut down for longer outages, consider two things. Get a UPS that communicates with your PC so your PC can shut down on its own, and consider not hooking your monitor up to it. If it's a blip, you can wait for your monitor to power back on, and if the computer shuts itself down, you don't need to see anything, especially considering how much power CRTs suck down.