You shout do with step by step

First step take your Netscape to know Thai font.

1.              First , check you windows it have a Thai font now.(If you don't have a Thai font  to get Thai font)
 
2.              Okay, if you have Thai font now open Netscape Composer and then look at the Edit  click Preferences .
 
3.              In the next step you can see a new window(on head it write Preferences) and look at the box on the life hand .(your hand)
 
4.              You can see alot of think on the box find an Appearance and then look to the Fonts and click it .
 
5.              In the Font look at the top right you can see For the Encoding: and it have a box near in the box it is Western click the down arrow choose User-defined  and then in  Variable Width Font: change it to Angsana UPC or any font name have "UPC" in the back  (UPC = thai font ) next in Fixed Width Font: choose CB Thai Test Font (if you have ) but if you don't have look to the name have "thai" if you look around and can't find it don't worry it is okay .
 
6.               In the last step , look down to the Some times a document will provide its own fonts. Then click Use document-specified font,including Dynamic Fonts . Then click OK bottom

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Last step read thai font in thaiweb.

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7.               When you come to thaiweb and you can't read it choose View.
 
8.               Then choose Encoding and choose Use-defined.
 
9.               The Netscape will road again and now you can read thai.