Win95(98?)
You can use Thai on an English version of win 95 (or 98 & NT ?)with the addition of a programme and some fonts.The programme is necessary to translate the UK keyboard to the Thai keyboard . I have used fonts from the TSM
package mentioned below but the following links provide FREE fonts and software , http://thaigate.nacsis.ac.jp/ftp/thaisoft/titech-aima/. Pick up the following downloads , thaikdb.exe & the font package .
Win 3.x
For windows 3.x users(I'm sure there must be some left ) there is a package called TSM for Windows by ThaiSoft which supplies the fonts and software .The fonts can be used on win95 but not the software .There is a link ...PUT LINK HERE ...but this just references a telephone number .