Dell * XPS 410 Mini-Tower:
*Intel Core 2 Duo Processor E6300 (1.86GHz, 1066 FSB)
* 512 MB DDR2 SDRAM 533MHz (2 DIMMs)
* 160 GB SATA Hard Drive (7200RPM)
* 16X DVD ROM Drive
* 256MB nVidia Geforce 7300LE TurboCache
* Corel Paint Shop Pro XI - Advanced photo editing
* Windows Vista Home Basic
* One Year Warranty
or eMachines T5224 Minitower
*Intel Viiv Technology, Intel Pentium D Processor 820, 2.8GHz,
*250GB Hard Drive,
*16X DVD+/-RW Drive,
*Windows Vista Home Premium
Something to keep in mind - in the future, she may want to do more than just the Office and internet basics with her computer. What seems adequate and fast right now, could seem terribly slow in the future as you go on to more advanced software and tasks. For most people, it's best to try to squeeze in the extra RAM and faster processor when you first buy the machine. The extra money you spend at the beginning will be forgotten 6 months down the road. Upgrading is always an option but with an economy computer, upgrading may be expensive due to out of date components. Of course, it also depends on if you will actually take the time (and be willing to open up the computer) to add more RAM or other upgrades in the future
I don't mean to sound like a computer salesman. Just trying to point out that a few extra dollars spend now will increase the usability as you learn to do more.
The devious move to make here is to give her your computer so you'll have to build a better one. Always have to stay one step ahead on wives- it balances out the times you will be wrong simply for being male.
Like someone mentioned earlier the XPS is the better of the two systems but definitely needs more ram.
As opposed to either of those you can probably get something of the X2 flavor considerably cheaper than the c2d and with no noticeable difference in the type of apps you mentioned. The cpu isn't as sexy as a core 2 duo but so what?
For that matter, you can go the extra mile and get an inexpensive core duo or turion x2 laptop. The cpu would be more than adequate (at least a gig of ram) and think of how cool you would be for giving her a laptop.
Either way, if you're ever going to upgrade to vista (even if you aren't) 1gb is a must, 2gb is better.