R help - Mar 2012 - substituting XML tags with custom values

Hello,

I have an xml document with a following element:

<sequence id = "ancestralSequence"> 
    <taxon id="test">
     </taxon>       
    ACAGTTGACACCCTT
</sequence>

I would like to parse a new sequence of characters inside the "taxon"
tags. I started looking into XML package documentation, but cannot find
a simple solution yet. My code:

# load packages
require("XML")

# create a new sequence
newSeq <- "TGTCAATGGAACCTG"

# read the xml
xml <- xmlParse("epoch_mcmc.xml")

# save as character:
charXML <- saveXML(xml)

-- 
while(!suceed) { try(); }