Help me buy a computer for a 70 year old

Hiya gang,

My mother is still plugging away on an ancient system that I gave her 10 years ago. Bits and bobs have been replaced, but the system is so old, she still has one of those massive CRT monitors taking up most of her desk. For her birthday and mother's day this year, I'd like to buy her a new system and a new monitor.

System needs to be able to run legacy 32bit accounting software. I'm pretty sure her current system is Vista, but I'm not sure.

She doesn't play games or do anything processor intensive. She runs a small accounting practice, she manages her own finances, and she surfs the web...for a given value of surfs the web. She doesn't like sitting in one position for very long, so I don't think she's a likely demographic for watching TV/movies online.

She has significant arthritis, laptops are not an option.

My budget is about $500 including getting to her in Florida.

She is not computer savvy at all.

I despise Dell with the white hot heat of a thousand suns, but if there is no better solution, I'll suck it up and force myself to give them money.