The pagefile size is a Windows NT issue. You should consult with a Windows expert on that question. I believe that pagefile size in Windows is recommended to be 1.5 times the real memory. However, in general, you should not allocate more memory to DB2 than exists in real memory, so making the pagefile size bigger may not be the best answer to DB2 performance problems.
DB2 performs much better in Windows 2000 and XP, as compared to NT (all other things being equal).
With regard to DB2 system and application performance tuning, there are too many things to list here. If you are not familar with DB2, either start reading the Administration: Performance Guide, or hire a consultant to look at it and also give you some skills transfer.
M. A. Feldman
IBM Certified DBA on DB2 for Linux, UNIX, and Windows
IBM Certified DBA on DB2 for z/OS and OS/390