ups trouble

Does anybody know what the typical wattage of a pc tower and a tivo are?

I ask this because I have an APC Battery Backup 350 (BE350U) and I have two pc towers (an old 486DX50 and a new AMDAthelonXP3200+) and one DirecTivo running off of the battery-backup outlets.  This device can handle about 350VA / 200W output, but every time the power goes out around here, the damn thing flips off about 5sec later (and must be turned back on manually)... also, it just flipped off for no reason at all only a half-hour ago.

Anybody have any ideas?

Those three in combination would be drawing way more than 200W. You're definately overloading it there. Most small UPS units aren't meant to drive more than one computer, and that particular model is practically a toy anyway.

Should I just use the two pcs on a single backup and a the tivo on second, or should I use one seperate backup unit for each device?

If you must, your Athlon should be on one device and the 486 and TiVo on the other (the Athlon will be the power whore of the three, probably sucking 250W+ depending upon configuration and load, whereas the TiVo will sip just ~40W, and the 486 under 100W unless you're including a monitor as well). Do bear in mind that at maximum power (which your Athlon will draw) the battery will die in a laughable 1.6 minutes according to the manufacturer's specs.