PC hardware--CPU & Motherboard & RAM/Laptop CPU question..
I've got a Dell XPS M1710 laptop, and it's been a pretty good one. Recently someone gave me a Dell Latitude E5500 laptop (hard drive removed), and it has an Intel Core i5 processor. Since the i5 is a newer cpu than the one in my XPS M1710, would I be able to take the dual core cpu out of my M1710 and replace it with the Core i5 from the E1550?
Simply put: no way. These two machines use dramatically different CPUs and underlying hardware, and are not intercompatible as a result. You could potentially put the hard-drive from the M1710 into the new E5500, but keep in mind you will have to re-install the operating system anew on the new machine. If the M1710 still works, you're probably better off just buying a new hard-drive for the E5500 if you'd like to use it (they're not horribly expensive, especially if you don't need a lot of capacity).
Laptops are generally not designed to be upgraded (or repaired) in this manner, and that's the biggest trade-off made for their mobility. On newer systems, most components are even glued/sealed to the machine to explicitly prevent what few user upgrades/modifications could be possible (the idea being to maintain a monopoly on factory BTO configurations, which often have significant price mark-ups).
Even given its age, the 1710 is still a fairly powerful machine; the biggest limitations will be on the GPU and its lack of support for DirectX 10/11, and its partial video acceleration support (that is, while it can assist with decoding h.264 content, it cannot fully offload h.264/VC-1/HEVC/etc content like newer GPUs can). If you're not doing a lot with video, and don't need to run DirectX 10/11 games, I don't see any glaring problems for the 1710 as long as its been kept up-to-date with a supported operating system and associated patches (this suggestion is primarily for security reasons).
If you're after a new machine, however, you can easily buy something today that will offer comparable-or-better performance than the 1710 in a much lighter package, and get better battery life to boot. Alienware (Dell's high-end gaming computer subsidiary) would be where I'd start the search if you're looking for something that's most analogous to the 1710, but if you aren't after gaming performance, a contemporary ultrabook will offer significantly better battery life and size and cost a good bit less than a high end mobile gaming system.