How to tune the latex for different compilers?

[Angus Leeming]

Reading the 'tex4ht' documentation, I find that I should wrap my 
'XFig' pictures inside a '\begin{mypicture}...\end{mypicture}' block 
so that 'tex4ht' can recognize the contents as a single image and 
therefore generate a .'gif' file containing the compiled '(.pstex_t, 
.eps)' image. (Works well BTW.)

For 'tex4ht', mypicture should be defined as:
        \newenvironment{mypicture}{\Picture*{}}{\EndPicture}
where 'Picture' is something defined in the internals of 'tex4ht'.

However, this environment is senseless to the 'latex' and 'pdflatex' 
compilers. I find that this works perfectly:
        \newenvironment{mypicture}{}{}

My question: Is there a way to wrap these two definitions inside
        if (<compiling with tex4ht --- htlatex, actually>)
                \newenvironment{mypicture}{\Picture*{}}{\EndPicture}
        else
                \newenvironment{mypicture}{}{}

so I don't need to edit my preamble before launching the compiler?

-- 
Angus