Lets assume that MSISYS.VXD is the missing file and you need to replace it Open a command prompt and type:
extract /a/l C:\temp D:\win98\base4.cab MSISYS.VXD
D: assumes that D: is your CD-ROM letter so substitute the drive letter names to reflect your system .
Base4.cab is the first file in the series of CAB files. The /a switch tells the extract program to look through all the files until it finds the one you want.
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