Linux on an old PC

I use my old Dell 2400 desktop PC primarily for printing from my HP Deskjest 6940 printer, and scanning from my Canon Canoscan LIDE 30 scanner, because they are not compatible with my Windows 7 laptop.
I also use a MediaLink WiFi Dongle to connect to the internet with it.
My problem is the Dell, which runs XP, is becoming slower & slower. Using it really tests your patience.
I'm debating about installing a Linux OS that is compatible with old PC's ( this is one is about 9 years old approx. ), such as Puppy Linux.
I'm seem to recall that most printers & scanners will run OK on Linux, but I'm worried about the MediaLink wifi dongle working on it.
My previous experiences with getting wifi cards to work with Linux have not been fun. Any advice would be welcome.
Thanks.