Windows 98 wont load-need old data files

I have a WIndows 98 machine and when I tried to load windows it told me himem.sys was missing. I loaded the file from another machine but now it says to reinstall windows and wont let me do anything. I need some important files off the computer. I can’t get them from dos because they are large. Can I reinstall windows from the cd and still keep all my files safe on the computer? Will it ask me if I want to keep the old files. Please help! Thanks,
George