My c:\windows\temp file is by now over 40 Mbytes long. Is it safe to
delete it or is it needed to maintain all the information on the hard
disk?

My computer is a pentium with windows 98

vaac...

It's perfectly safe to delete everything in the temp folder
c:\windows\temp that you specified. This is a temporary 
folder used for files of a temporary nature, such as those
used during the process of installing a program. Once the
program is installed, the files in the temp folder can be
deleted at will, and it is recommended that you do so in
order to reclaim hard drive space. Delete the contents,
but leave the folder. Windows uses it on a regular basis.

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sublime1-ga

Do not want to delay rating longer. Did not have chance to check this
out but your answer seems to agree  with evething I hear, Thanks.