For computers with memory ( RAM ) less than 200 Mb, not many versions of Linux are suitable.
Xubuntu http://www.xubuntu.org/
is considered to be complete and simple. and it is based on ubuntu, and you have many programs available for it.
You can run it from a FAT32 or NTFS partition. It will even reside in a folder with in Window if you do not want to get rid of windows and still not create a second partition.
Depending on the version you wish to use with Puppy Linux, it can be as small as 40mb or up to 200mb+ in size.
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