My Arduino is warmer than I like

Long story, but I bread boarded and then made up a board with an Xbee and DS1620 chip to send the temperature to a central unit. It works great while I had it running off the USB power. When I moved them out to the field and connected them to a 9v supply, the unit warms up about 3-5 degrees.. I know, I know, move the Ds1620 off the board. But I went to a lot of work and was wondering if anyone had a brilliant suggestion.

Add an LM7805 Voltage Regulator so the 9 Volt is brought back to 5Volts. e.g. http://www.sparkfun.com/commerce/product_info.php?products_id=107 Please note the minimum supply voltage is 7 volts.

So basically move the 5V regulator off the arduino board? Can I just run the 5V into the 5V pin instead of the power plug?

So basically move the 5V regulator off the arduino board?

That is exactly what you are doing. Instead of using the on-board regulator you use an external regulator. The upside is that the Arduino board won't run as hot, the downside is you haven't reduced your overall power dissipation. So if you are in a box or similar enclosure you are going to see the same amount of total heat.

Can I just run the 5V into the 5V pin instead of the power plug?

Yes. You can put in regulated 5V on that pin.

You can use a switching regulator then it won't get hot:- http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=152-524&x=0&y=0

Or pololu.com if you're in the US http://www.pololu.com/catalog/category/84

Found one on ebay too http://cgi.ebay.co.uk/POLOLU-STEP-DOWN-VOLTAGE-REGULATOR-D15V70F5S3-/170549099784?pt=LH_DefaultDomain_0&hash=item27b584bd08#ht_2213wt_905