Sharon, my dear friend - how wonderful to see your ThinkPad family growing so steadily! Soon you will be "ThinkPadMom5"!
I assume that the R50 which your son #2 is presently using is
this one and if so, and if it still has the original CPU (Pentium-M 1.6 GHz/Banias), as well as the original harddisk (60 GB/4200 rpm) that it came with when you bought it, then these two things in combination will certainly tend to make it feel somewhat slow, if compared to more modern ThinkPad's with faster CPU's (such as T42's with 1.8 GHz Pentium M's and upwards to e.g. T60's with newer Core Duo CPU's), and not the least when compared to machines with faster drives (either 7200 rpm's or the newest generation, almost-as-fast 5400 rpm with very bigger cache memory and higher data density).
Anyway, in order to be best able to comment your question, I kindly ask you let us know what of these requirements/specifications are most/least important, and which are perhaps even totally unimportant:
1) Any special
requirements beyond normal college work (writing, misc. educational programs, surfing, watching movies)? What would you say is the anticipated use; now, and well as in, say, 3-4 years ahead?
2)
Remaining IBM/Lenovo warranty: Is this don't-care/desirable/somewhat important/absolute requirement? Are you OK with buying an out-of-warranty laptop?
3)
Size/weight/portability: Is small size (and/or low weight) an issue of importance, or will the laptop only be carried on shorter distances (e.g. within college), such that a relatively "big" and "heavy", say, 15" ThinkPad is no problem? In other words: Are all options open here – from the biggest, largest, heaviest 15.4” widescreen models and down to the small, ultraportable (but small LCD!) 12.1” models?
4)
LCD size: Is of course strongly linked to the above; What do you think is sufficient and what will probably be too small; is e.g. the X-series ThinkPad’s (12.1” LCD’s) too small?
5)
Display resolution: Will WUXGA or UXGA be acceptable, or do you prefer to stay with WSXGA+/SXGA+? Some users experience eye-strain when going to very-high resolution LCD’s, but high resolution may be acceptable to younger eyes, such as you sons? (I believe that the higher-resolutions however are more power-consuming, meaning slightly lower battery time).
6)
Battery time: Is very long battery time a necessity, or will there be access to AC mains most of the places where the laptop is to be used?
7) Is a
built-in CD/DVD-RW required, or is it acceptable that the laptop does
not have this so that it
needs to be placed in a dock that has a CD/DVD-drive?
8 )
Noise level? Some users are more picky about fan and disk noise than others; how's your son #2 about this? (if fan noise is a potential source of annoyance, laptops with so-called "integrated" graphics are better, since they consume less power compared to so-called "discrete graphics" models - but the latter are faster, and chosen by people with high requirements to graphical performance; be this either technical applications or gaming).
9)
Operating system? Will the laptop
need to be capable of running Vista (now or later), or is XP sufficient? If Vista-capability is not a requirement, then I would absolutely recommend XP; it runs faster, it is easy to use, and your son is already familiar with it from his present R50.
10)
How long do you wish this laptop to last? Are we perhaps talking about getting another, newer, faster laptop in a year or two - or how long would you like this new laptop to remain usable?
These were just a few, quick questions – which may hopefully help to lead us onto the right track!

And, hey, remember that we
ALL surely want to see this, your "new baby" to be one of the absolutely most beautiful ones, ever!
Kind regards,
Johan