You may want to look at something along the lines of a line-conditioning UPS.
Some of the straight battery backup UPSs tend to not switch fast enough to the battery to prevent shut-down and data loss. We've had a member that had some severe trouble with this problem due to the sheer number of power interruptions they encountered.
Plus the Macs tend to be somewhat sensitive to line noise and brownouts (low line voltage due to overloaded circuit, or power company.)
And the big PowerMac and a CRT are probably going to require the bigger UPSs than people typically buy or have in the closet.
There are a few older threads on this topic, so a search should yield some data -- I've posted in quite a few of them so an advanced search on UPS and Member/Sun Baked should narrow it down to some of the juicy threads that included some of the actual Watts used real quick.
Probably the 1000-1500VA UPS for a start, depending on what else you'll be plugging in to it -- but, it's the maximum output wattage that's key, not the VA.
For size, the 725 might be big enough, but you should probably get the 1000.
Remember quality costs some money. Also remember what the UPS will be protecting.
Another thing to note is that you don't need to (and probably shouldn't) install the APC software. Mac OS X as of 10.3 has UPS monitoring built in. When the Mac recognizes a UPS, the Energy Saver Preferences Pane will have options for the UPS.
I highly recommend APC, American Power Conversion. Currently using three of them, completely satisfied with there performance. My recommendation would be to contact them directly via the web or phone. A technician will be able to find a product that best meets your needs.
yup..my APC Battery Backup 1000/1500VA 600/865 Watts... its the RS BR1500
it's sitting right here about three feet from me in its brand new factory box..I'm thinking and hoping I got the right one...I got it for $178.22 delivered from eCost...I don't know why it says 1000/1500VA 600/685 Watts instead of just 1500VA 875 Watts...its called RS 1500 ..the big day is drawing near for me..I got a Linksys wireless router today too...I'm going to hook it up as a wired router for my existing PC and my new G5 Power Mac 2.5 with the wireless in place in case I want it or need it...oh happy day...pretty soon...