The “rpm -aq” command can be used to query the list of RPMs installed in the system.

[neo@techpulp ~]# rpm -aq
gnu-regexp-1.1.4-10jpp.3.fc8
java_cup-manual-0.10-0.k.6jpp.1
ql2200-firmware-2.02.08-1.fc8.1
popt-1.12-3.fc8
freetype-2.3.5-3.fc8
sed-4.1.5-9.fc8
libattr-2.4.38-1.fc8
device-mapper-1.02.22-1.fc8
libIDL-0.8.9-1.fc8
....
python-xlib-0.13-3.fc7
qt-designer-3.3.8b-2.fc8
[neo@techpulp ~]#

You can use ‘grep‘ command to search for a particular RPM in the list as shown below.
In this example, we are trying to find if the GIMP package is installed in the system.

[neo@techpulp ~]# rpm -aq | grep gimp
gimp-libs-2.4.0-0.rc3.2.fc8
xsane-gimp-0.994-4.fc8
gimp-2.4.0-0.rc3.2.fc8
[neo@techpulp ~]#