I have been doing some work in Arduino IDE on an old laptop I have been using for field work. Arduino worked painfully slow (eg. opening menus blocked any work for almost 20 seconds), but I didn’t think that the laptop (with its rather dated 900MHz Celeron processor or the old Windows XP) was at fault as the previous version of Arduino IDE worked almost flawlessly.
A quick search thru internet provided evidence that the supplied rxtxSerial.dll file has issues with scanning serial ports if you have bluetooth COM ports or virtual COM ports installed. ( http://www.johngineer.com/blog/?p=97 ). The same problem can be experienced with some terminal software, eg. RealTerm, however that software only preforms the port scan once and allows you to abort the process of scanning ports.
To fix this issue you need to replace the original rxtxSerial.dll file with a new / fixed version. I suggest you to just rename the original file (eg. to rxtxSerial_old.dll) in case the new file doesn’t work as it should.
The fixed version may be found here:
Please note that the file is not hosted on my site, so I can not guarantee that it will stay there or that nobody will modify it. I suggest that you have a antivirus active when downloading and using executable files from any online sources.
The link to the latest version and the source code also can be found in authors original posts on arduino forums: