You mean, apart from using the pretty graphs in vCenter?
The simplest option is to run the command
# esxtop -b > esxtop_whatever.csv
This will make esxtop run in "batch mode", outputting data into CSV format.
(See also: http://www.jume.nl/esx4man/man1/esxtop.1.html)
You can then load this file into perfmon on Windows or use esxplot (http://labs.vmware.com/flings/esxplot) to view the data.
Another nice trick is to create a performance snapshot (http://kb.vmware.com/kb/1967)
# vm-support -s -d <duration> -i <interval>
This will create a large file with a number of 'snapshots' of the system state. This can then be 'replayed' with the command
# esxtop -R .
in the extracted TGZ file that was created in the previous step.
We use that one quite a bit for performance troubleshooting at VMware ;-)