As everyone else says. If you try and play the Infocom games in their original incarnation for any given OS, then yes, it’ll be difficult. But the games themselves exist as data files as well, usually in the form zork.dat, or zork.z3, or zork.z5 (and some games are .z6 and z.8). Depending on your source for the games you may have them all in .dat files*. You can load them into any modern Inform interpreter, as zarf says and links to, and it’ll be über-easy.
*[rant]I got a huge collection of Infocom games, unadvertised, when I bought the Zork Anthology. Zorks 1-3, BZ, Z0, RtZ and Nemesis… and a mysterious folder full of .dat files with names like SUSPENDED and SUSPECT and INFIDEL. I was thrilled when I found out they were games… but it didn’t do me any good because there was no documentation![/rant]
Re “spending a lot of money”, I’d advise you to ask around, in this forum, what exactly you’re looking to acquire. I know that at least one collection - a volume of the Lost Treasures of Infocom - had very bad quality manuals, and was even missing, for Ballyhoo, a piece of information without which you couldn’t finish the game.
Now, if you’re talking about spending a lot of money because you’re going to buy a packaged version of the game in eBay for hundreds of dollars… then yes, you’ll have difficulty getting THAT one to run. I wouldn’t reccommend it unless you’re a collector.
I don’t know about the original versions, but this wasn’t true even of the DOS versions I played of Infocom games. Of all the DOS IF I’ve played I can only remember THE MIST (and maybe BEYOND THE TITANIC, but I’m not sure on that one) as games that forced you to save on a disk (but if you go to other systems, like Apple II, yeah, you need the separate disk. Unless you have an emulator, which is what you probably have).
Argh, rambling, drivelling. Back to the point: the number of DOS games I’ve played where you could ONLY save to a floppy disk can be counted on the fingers of one hand, and none were Infocom’s.