Disclaimer: I'm a programmer but not super knowledgeable about hardware specifics so this is more a layman's answer.
I think making say a wire that could meaningfully transfer input/output via USB would be relatively simple (assuming they had the material science to develop a usb cable) the hard part, especially if they don't have an understanding of english would be making sense of the file system and data.
If they only have one laptop to work with it would be a lot harder to get meaningful information safely. A modern hard drive probably couldn't be analyzed by tech from 20 years ago without dismantling it and even then i don't know that it'd be readable.
It's likely they could make some intelligent guesses as to how the OS works based on their own systems. Set up a series of tests (writing the same simple text file 1000 times to the hard drive so their machines may detect how that pattern is stored and encoded allowing them to learn more about how the hardware is storing information)
I think there would be 2 scenarios
The scientists learn as much as they can taking detailed notes and then proceed to dismantle the computer they would likely be able to understand some of the concepts and push forward their own tech but might lose the data on the device.
The scientists learn as much as they can without dismantling the device and then store it until their tech is on a more similar level or perhaps a little ahead. They can then make educated guesses as to how the file system and interface protocols would work and understand enough of the hardware to clone the hard disk without loss of meaningful data.
I think the key to understanding the laptop and how it stores and processes information would be finding patterns in the storage device that you can trace back to meaningful content. If they can figure out what "tents' looks like on the harddrive they can start to understand how information is encoded and stored. then they can figure out what a file looks like on the drive.
Realistically i would look at what your goal for the scenario is and play to that. It's unlikely they 20 year old tech with no common base would meaningfully interact with a current computer. So if they need information on the computer they should maintain the computer to learn from it.
If the data isn't important and the laptop is to allow one group advanced technology they develop their own technology based off the hardware but still independent.