for font size we need to use px or pt ? eg. 8 px or 10 pt and what about table width should be in px or in pt
8px text will be impossible to read, as will 10pt text (though 10pt text will be near-impossible). Rather than setting your font-size in either px or pt, why not respect what the user has their font size set to and base your document structure off of that?
If its a fixed width layout, go for pixels. If its elastic/fluid then go for ems/percentages. Just make sure the text is readable, like minimum font size for Arial IMO is around 11 or 12, 10 is unreadable.
You can still use %/EM on a fixed-width layout (via the BODY selector), but you should use px for everything else (again, on a fixed width layout).
You may want to read my post here on the subject: http://forums.digitalpoint.com/showpost.php?p=3688881&postcount=2 Again with the crowd, anything less than 12px is a total /FAIL/ - and I usually consider 14px minimum for anything content related... Though I prefer 10 and 11pt since those obey the "system metric" in every browser.