According to these specs
your Acer has both an HDMI and a VGA (aka D-sub) video output."HDMI port
for connecting to a compatible HDTV or home theater receiver for uncompressed digital audio and video via a single cable. Also includes standard analog VGA video output. "
So while you should be able to connect this to a HD TV with an HDMI input (using a HDMI cable), what you really want to accomplish is connecting it to the Dell monitor - if I read you right. I would expect the 7 year old dell 21" monitor to have a VGA (analog) input, but suppose it's possible that it has a DV-I (digital) input. A VGA cable should look like this
while a DV-I connector would look like this
The model number of the Dell monitor (should be on a tag on the back) would be helpful in looking up what type of input connector the monitor has.
The USB connectors won't be of any use. Your best bet (if the monitor has a DVI input) is probably a HDMI to DVI cable such as one of these
to connect the new Acer's HDMI to your older Dell monitor.
Edited by Bill253, 19 March 2011 - 08:46 PM.