Drop Tables Very Slow in Postgresql 7.2.1

Hello there !!!

I am using postgresql7.2.1 as the backend for an E.R.P system running
on Linux Redhat 7.2(Enigma)
The database size is around 20-25GB
Dropping of an individual table whose size is around 200Mb takes more
than 7 mins, and also increases the load on our System
The database is vacuumed/ reindexed on a daily basis.

We have recreated the same database on a Linux Redhat release 9 OS, and
used PostgreSQL 7.3.2, the drop here is really fast.

Any suggestions as to how I could improve the performance of drop on
postgresql7.2.1.

Thanks
maneesha.