No problem regarding the question on the memory. :) I used to buy other brands, but I bought GSKILL once, got good results, and looked them up on Wikipedia and discovered they were an A-brand. Typically with older, non-overclockable machines, it's most important to have matched memory of the right speed; mix it, and the operating speed may shift down.
SSD refers to a Solid State Device, a replacement for a traditional hard drive that uses memory rather than spinning platters to store data. It's much faster than a traditional hard drive and will give a huge boost in performance and responsiveness. Since SSDs are much more expensive per unit of storage than traditional hard drives are, their use tends to be restricted to boot drives. If you were to buy one and later buy a new computer, you could move the SSD over; most new computers are not so equipped and an SSD makes a big difference.
I'm not sure why the 3100 hangs, but bad memory is a potential cause, as is a flaky power supply or a problem with the motherboard. I repaired a freezing, slow-performing 5150 some time back, and it was due to the power supply.
If you were wondering, fixing and hot-rodding old Dells is a hobby of mine.