Your comments

Possibly. But I've added support for Firebug Lite in Textastic 4.0. I'm going to submit this version to Apple today.
Note: it's just the @import directive that doesn't work for local files. If you enter a complete url like
@import "http://www.example.com/test.less"

then it does work without modification.

Unfortunately, there is not much I can do about it. This would need to be changed in LESS, so that it doesn't hard-code supported schemas but checks if the path starts with <schema>:/

The problem is in the "loadStyleSheet" function of LESS: https://github.com/cloudhead/less.js/blob/master/dist/less-1.2.2.js#L3079


Textastic uses the custom "preview://" protocol, not "file://". This is needed to work around a caching but in iOS 5. 


So if you the change regular expression in this line:

if (! /^(https?|file):/.test(href)) {

to

if (! /^(https?|file|preview):/.test(href)) {

then it works for me in Textastic.

The basic sample works for me as described in my last comment.
I've just tried it out and it works fine for me:


test.html:

<!DOCTYPE HTML>

<html>
<head>
<meta charset="utf-8">
<title>Less Test</title>
<link rel="stylesheet/less" href="style.less" type="text/css" />
<script src="lesscss.js" type="text/javascript"></script>
</head>
<body>
This is a test for lesscss. 
</body>
</html>

style.less:

@color: blue;

body {
color: @color;
}

I've put the lesscss.js in the same folder as text.html and style.less. This resulted in blue body text.

Can you please explain in more detail what you are trying to do? 

You can access your Dropbox using a remote connection as explained in the manual: http://www.textasticapp.com/v3/manual/lessons/How_do_I_access_files_in_my_Dropbox_account.html
Due to sandboxing restrictions in iOS, an app can only access its own files. So this won't work, unless I'm missing something.
You can also just try out this T-SQL bundle: https://github.com/adamv/tsql.tmbundle (I found it by searching for "t-sql tmbundle")
You can find documentation on TextMate Language Grammars on their website: http://manual.macromates.com/en/language_grammars

There is also a book on the subject: http://pragprog.com/book/textmate/textmate

The SQL TextMate bundle can be found on Github: https://github.com/textmate/sql.tmbundle

Textastic loads the Syntaxes/SQL.plist file.