The external enclosures can hold IDE drives just fine, and it'll feed data to a USB2 or Firefire port. I had an enclosure on a IDE drive back when it was still USB1 (2000), worked fine but slow.
These days, there are certain controller chipsets you want to look for and avoid.
Prolific chipset is often complained about.
Oxford chipset is often praised and preferred.
Cypress has mixed reviews, newer ones seem better.
Pricerunner.co.uk and
Amazon.co.uk might be helpful for shopping.
Learning which enclosure has which chipset is a matter of reading the item description and hoping it's there. If not, type the brand/model into google, and try to add the word "chipset" to the search. Or maybe pick the 3 main chipsets one by one and see if there's a hit for it.
Some people just get lucky, buy whatever they want for an enclosure, and it simply works. It's a gamble, but it works out for some.
I'm also not sure if chipsets matter as much anymore. It's honestly been a while since I've seen folks whisper about this topic. I've not looked into it since 2006, as most of what I buy these days is already enclosed by the manufacturer (Seagate, WD, Sony, Pioneer). I trust their products to work right away, and they do, no worrying about enclosure cooperation. Honestly don't even know what is in the guts of those enclosures.
Your computer looks fine, and I commend you on using Firefox. Just don't AdBlock my one site ad.