Linux - it may be the answer, but it's hard work!
I made my "old" PC into a Linux machine a year or so ago, to learn this new stuff. The good news is that Linux is (mostly) free. The software that goes with it is free, and very competent.
The bad news is that it's a lot geekier than Windows: you have to type the "admin" password every few minutes (or sometimes less) if you're trying to set anything up. Installing software is (mostly) a nightmare if you don't speak "job control language" - there's one example of how to install a simple graphics package
here. In contrast, I use a similar package for Windows: to install that I had to run the setup.exe - and that was it.
When I got stuck (which happened often), I asked on various Linux forums. From those, I learned above all that a) Any idiot can do it; b) I'm stupider than any idiot, and c) What do you want to do that for anyway? When I got to the hard questions, the only responses I got were "I have the same problem - did you ever find the fix?" I still get those to this day.
Then I found one super guy who really knows this Linux stuff and is supremely capable and helpful, and no, I'm sorry but I'm not passing on his details.
There are many flavours of Linux to choose from; the aficionados call them "distros". I tried four distros before I got one that actually worked at all. The one I have (Debian) is pretty solid and stable, except that most of my peripherals don't work (ie printer, soundcard, scanner, webcam, and joystick). Some can be got to run by opening a command prompt and typing a load of JCL at it - but that only works till you reboot the machine, then it all has to be done again. I tried to write "startup" batch files to do that automatically, but it doesn't seem to work like that.
Connecting to a network is easy for the Internet access bit - it took me less than four hours to set up the Internet so that it could browse and send/receive e-mail. I doubt I had to type the supervisor password more than 50 times in the process.
But the network interface (called Samba) is something else. After about three months, I managed to cheat it enough to get it to talk to the other machines on the network and transfer files around.
There's a very clever package (called Kpackage) that will download the full list of all software available for Linux, and install it for you without any of the JCL stuff. The only slight snag is that 80% of the install processes end with an error message that it wasn't able to complete the job. Usually the reason was in Klingon, but often it told me I hadn't got the right version of something else. That meant load another item, which in turn needs another item which...
The killer for me was when I'd at last got enough stuff working to be able to use it "in anger". At that point came the time to upgrade to the new release that promised lots of fixes for the "doesn't work" items. Ah, no, you can't upgrade. You start again from scratch and install everything. Yes, right.
At that point I dug out the old Win2000 CD and loaded that onto the machine in "dual boot" mode. For playing, Linux is a challenge. For doing serious work, and for "server" duties, it's Windows.
I'm assured by those who can drive it that there are reasons why all those pitfalls and obstacles are there in Linux. I'm sure they're right. At my age, life's just too short...