You should warn people on the site content (it's normal practice in these forums to add a line to your post - WARNING: adult content)
Anyway... as I see it your html syntax is not great...
IN IE6 and FF - the only difference I can see is the white text in your "welcome message" is not appearing...
e.g. my guess this is due to no closing tag for "</font>"
and you are using capitals in your syntax.
Try something like:-
<font color="#fffff" size="2">Welcome<br />Introduction to our site is as follows<br /></font>
But it would be even better if you used style tags (CSS) and called those instead of doing html inline only e.g. class="Welcometext" (and put the font attributes in that style in your CSS sheet).
I also suggest that you run through the errors you get for w3.org a bit closer - as seeing your html code, a few of them are probably real errors.
Hope comments help... cheers - Asiaplay
PS: if you ware talking about other fonts... which perhaps are not showing on my browser at all...
i.e. you have changed something else to use a special font (then please note that I am not seeing it in either IE or FF!!!...
Do make sure you stick to standard fonts e.g. arial, tahoma etc. - this is as fonts rely on the person having a font loaded on their PC and for FF, it is not possible to change font used easily I noticed i.e. each language uses a default font, which is used if the specified font is not found on someones PC (if you want to use some special font, which is not standard, then you will have to use a jpeg, with an alt tag).