In the movie "Elizabeth", there is a character who dies after she
wears a poisoned dress. I am wondering if that could really be done,
whether it's historically accurate, and what exactly it means to
poison a dress.

Here's an interesting thread discussing the poisoned dress in "Elizabeth":

http://imdb.com/title/tt0127536/board/nest/15467337

A recent episode of "CSI: New York" involved a bride who died because
her wedding dress (bought from a resale shop) had previously been worn
by a dead person, and embalming chemicals had seeped into the dress.

The CSI storyline was probably an adaptation of an urban legend described here:

http://www.snopes.com/horrors/poison/dress.htm

In the 19th century, dressmakers were known to die because of
chemicals used in manufacturing fabric. So fabrics that are "poisoned"
and come into contact with the skin can definately cause injury and
death.

Kriswrite

Definitely. Remember that your skin and therefore your body absorbs
everything that you come in contact with especially if it is solid or
liquid, not too much gaseous matter. This is very true in times od
prolonged exposure or when the pores on your skin are most open, after
a shower or heavy sweating.

Poisoned clothing appears to be possible and involves impregnating the
item of clothing with a toxic substance which is absorbed through the
skin or inhaled. There are a number of hits on poisoned clothes being
used to kill soldiers in South Africa.

The specific Elizabeth dress incident you mention is not historically accurate.
http://www.elizabethi.org/uk/faq/two.htm
 
Reports of death by wearing clothing soaked in embalming fluid are
listed as urban myths.
http://www.snopes.com/horrors/poison/dress.htm

- Hammer

Only certain poison's can be absorbed through the skin. Or a agent
that opens pores must be used.

Using this You maybe able to find out if these kind of poison's were
in the area of london in the Elizabeithian time.

There are several plants that release toxins.  Hidden in a corsage,
for example, such plants could trigger anaphalatic shock.   Too many
kids, and adults, have died from a stray smear of peanut butter, or a
random prawn shell in seafood soups.

It's a common enough theme. Do a quick google on "poison cloak" instead.