I presume the item you are talking about is specifically made to adapt hard disks from a laptop into a traditional desktop PC. If not - you might consider a hard disk enclosure made specifically for this purpose.
What I suspect has happened is Windows is not "seeing" the drive because you've never installed it before.
As Delaney said, go into Computer Management (Under the "Administrative Tools" section in Control Panel, make sure you're using Classic View - not that dopey modern view XP introduced) and a drive should potentially appear there.
If the drive show itself as "Uninitialised," then this indicates Windows is having trouble recognising the partition table and at this point, the data may not be recoverable. If you partition the drive (BE CAREFUL! PROCEED AT OWN RISK ETC!), you may be able to use data recovery software and retrieve what is present.
What I might suggest is paying for data recovery if this happens to be the case. Not worth diddling with because it can sometimes end badly. I've screwed up a number of times due to misunderstanding, and I'd consider myself something of a computer boffin.
Now...
Whether Windows XP is supported or not is irrelevant to the discussion.
A hard-disk is a hard-disk (except for the >1TB models used Advanced Format which I'm sure are not the subject of this discussion) and data retrieval trumps any OS support.
FWIW I still use Windows 2000 here at home - works great on the hardware I prefer to use and I've not managed to infect myself despite "doom and gloom" from experts (or "experts," depending how you see it).
Heck, W2K even ran my personal website for a couple of years and all it ever saw were random attacks designed to compromise PHP or IIS.
Modern internet routers and even basic modems have NAT and Firewalling capabilities which essentially block simple access to a system that would allow Worms and Viruses of the past to find their way in - which exploited computers because of the fact computers were practically "naked" on the internet.
Windows Updates are designed to cover those bits up and "secure" Windows from these holes. Fire-walling and NAT blocks that easy access simply by denying access to the system as a whole from the outside. This is why for very specific applications, you have to manually open specific ports in order for them to communicate across the internet.
Most infections today rely on user being gullible and clicking on malicious advertisements (these even appear on well-reputed sites like Forbes, which is why I Adblock) or blindly installing software to their PC's.
You can't fix stupid, and neither can Microsoft. Newer versions of Windows are just as infectable as the older versions. Some people can infect their new machines in minutes...
Back on topic, now guys.
