Office 2007 programs very slow to start up

Hello, I recently upgraded a number of the computers here in my office. During the process the users were also upgraded from Office 2003 to Office 2007 (a fresh full install that came with the new computer). Since then, two of the systems have developed a problem whereby Word or Excel (and most likely Powerpoint), whichever one is launched first, will take anywhere from 5-10 minutes to complete loading. During this time, the Word or Excel program is completely frozen, with a large plus sign visible on the screen. All other programs function normally during this time. Once either Word or Excel has launched completely, for the first time that day, both programs will fully launch in the usual 2-3 seconds. The only software I can recall installing, prior to this problem starting, is Windows SP3 for XP, but this was done to other computers running similar, if not identical setups, and the other computers have not had this same problem. I have been conducting regular searches for the last 6-8 weeks on the internet, but have found information on this problem. Does anybody have any ideas as to what may be causing this?