C) getting it past the wife (this is the biggie) , as she says on the comp too much already
Welcome to our world... we're all on the computer too much already!
You're right: getting the right RAM is very important. You don't want to waste money (or time) buying the wrong thing. Determining what kind of memory may be the easy part. But we also need to determine how much RAM is your maximum. There's also no point in buying 4 GB if the motherboard will only allow up to 2 GB.
You can open up the case and remove the RAM, and see if the info you need is printed on labels on the chips. But there are some software tools you can install on XP that will help you determine what kind of RAM it is. I'm not familiar with these tools, so you may want to try all of them to compare, or maybe someone else will verify one of them as better. They are
CPU-Z,
Speccy, and
Belarc Advisor. There are probably many other similar products too. These programs will likely tell you also if your CPU is 32-bit or 64-bit, so you can learn that for sure before downloading any Linux .iso files.
Now, how much can the computer hold? I don't know if the programs listed above will tell you that. Is it a brand-name computer, like Dell or HP? If so, let us know the exact model number... we can probably Google around to find the specs on that model and come up with the answer. If it is a home-built computer, you would need to open up the case and find the exact brand and model of the motherboard... so again a Google search might help to find the specs you need to know. The software tools above might also tell you information on the motherboard that will help to determine the maximum RAM.
If you open up the case, also at least note how many RAM slots you have and how many chips are installed. Also note if the slots are color coded... they sometimes alternate colors, like black-blue-black-blue. Back in older days, some RAM had to be matched in pairs, but it was also often installed in pairs even if not required. If you only have one chip, then it will be okay to replace it with a single chip. But if you have two, you should buy a pair to be safe.
If you get all the info and get ready to buy RAM, I would suggest that you remove the 256 MB that is there and not use it anymore if your can get a much larger set. You would not notice the little extra from 256 MB, but mixing with new RAM might cause trouble that you want to avoid (speed and timing issues).
Okay, I'm out for now. Other folks have good ideas too, so maybe they will have some better suggestions for you to move forward.
Cheers