Actually replacing the processor isn't all that much of a problem if you also replace the mother board with one that has the right socket and BIOS for the new processor, which likely will require an upgrade to the cooling system (or at least a new heat sink/cooler for the processor) and you might need an upgrade to the power supply - which may or may not fit in the case you have. ...

They sell kits for doing it. Search the web for "Computers - NEW."

Stupid sarcasm aside, your best course depends a little on what you mean be "getting left behind." If there are programs you really feel you need, that clearly require a later Operating System, you will need to take a look at what both the new OS and the new programs require, and whether what's really necessary is something your current machine doesn't have.

If your problem is more related to speed or performance for programs that just "run badly" rather than to particular functions, it's actually unlikely that you can make enough of a processor update (without a full motherboard replacement) to make much difference, since processor speed is seldom the "bottleneck" that really limits overall computer performance.

Changes like additional memory might solve some problems, and would be a lot cheaper than a new machine. If your hard drive is more than 2/3 full, it's even possible that a larger hard drive (with more free space) might overcome even some "program compatibility" problems, but that would be fairly rare.

Unfortunately, once you start trying out bit-wise improvements, it's easy to spend quite a chunk of money as you accumulate "improvements" that still leave you with an obsolete machine, so a new hunk of hardware may be cost-effective even if you could solve your immediate annoyances a piece at a time.

So far, you've asked if a solution would help without telling us much about what the problem is that you're needing to solve. About all we can really offer is a pat on the head and sympathy, based on what you've told us so far; but it does seem likely that you should consider a new computer along with any other things you might do to get what we'd suspect you really want.

John