New OS or computer?

I'm writing about my elderly in-laws' computer. It is an IBM Aptiva running 98SE. It has 128mb of RAM and a 20gb hard drive that is about 1/4 full. They only use it for email and internet browsing. My father-in-law also buys a tax program each year to do returns for the "little old lady widows from the church." He's a retired CPA. The programs he uses are H & R Tax Cut or Turbo Tax. Herein lies the problem. The day has finally arrived when their computer no longer meets the minimum requirements for those programs. The programs need Windows 2000, XP, or Vista. They want to know if they should buy a new computer or should they try to upgrade their operating system. I know their computer couldn't handle Vista, but what about XP or 2000? I'm inclined to disregard 2000 as I don't believe it is supported by Microsoft anymore even if I could find it anywhere to purchase. I haven't checked their motherboard to see if they have any slots for adding RAM, but if so, would that be a viable option to enable an upgrade to XP or Vista? They're on a fixed income, so it would be nice to avoid spending the money for a new system, but they are willing to do so if neccessary. I confess that I don't know myself what a new basic computer system would cost as I haven't been in the market for one myself for a few years.

Any advice will be appreciated.

Also, if by chance this is a duplicate post, please accept my apologies. I had some difficulties due to having to leave the computer for a few hours while writing this.

 

Thanks for the reply. Sorry it took so long to reply, but for some reason I can no longer get on this site from home, which is something I will address in another thread. I had to wait to get to work to use the computer there (shhhhh, don't tell.)

I guess I'll recommend a new system to my in-laws. At least maybe this will lessen the time I spend nursing their old system back to life when they have problems.