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There could be a couple of things at work here...
First off, what is the TYPE number of your system? That information can be found on the bottom of the system and should be in the format of 2645-xxx. It's also listed in the BIOS (Easy Setup) which is accessed by holding down the F1 key and turning the system on. Those two numbers should match. There's a very slight chance that somebody has swapped out the keyboard and what you see on the badge on the keyboard may not be what's actually inside.
Given that the two TYPE number fields you find are the same, plug it into the "Product number" field at this site:
http://www-307.ibm.com/pc/support/site. ... OME-LENOVO
That will tell you the configuration of the system. For example, a 2645-4AU will display this:
Product: ThinkPad 600E 2645-4AU [change]
Operating system: All [change]
Original description: PII 366MHz (256KB) 64MB RAM 6.4GB 13.3 XGA TFT 24X 56K(ACP) Win98
I'm assuming that you have used a retail (i.e., non-IBM) version of Windows 98SE for your install. If that's the case, the video drivers for the NeoMagic controller may have not been included and your system is running at VGA resolution (640x480). The 600E should have an XGA (1024x768) screen so I'm guessing that's the nature of your question. Downloading the video drivers from lenovo.com was the right thing to do. However, installing the driver is actually a three-step process.
This appears to be the video driver package for the 600E:
http://www-307.ibm.com/pc/support/site. ... SHY-3Y5LVT
It may help to first print out that page since it has all of the instructions needed to download and install the driver.
First step: Click on the vftprw8m.exe link. That should open up a window where you have to click on an "I agree" box and then you're asked if you want to save (or possibly run) the file. Choose "save" but you need to know where it is you're saving the file because you'll have to execute it in the next step.
Second step: Once the file has finished downloading, open up a Windows Explorer window in your download folder. Find the vftprw8m.exe file and double-click it. That will execute the program and it will create the files you need for the last step.
Third step: Open Control Panel's Display utility and follow the instructions listed in section II ,"Installation instructions for Windows 98". You will be telling Windows where to find the new driver information ("C:\DRIVERS\W9X\DISPLAY\").