There are lots of services which do not strictly speaking need to be running in most default installs.

as root, run

chkconfig --list > somefilename

That will save a list all services and their status, i.e. running or not, in each run level. If you post that list here, I or someone else can tell you the ones which you probably do not need(depending on when you post, I may or may not be around, but someone could help you).

I do not know what mandrake installs by default, but redhat does have quite a few services which are not needed in a default install. Of course this depends on what you are going to be using, if you do not use nfs for file sharing inside your network, you could certainly turn off portmap, nfs, nfslock, if you are not sharing files from your machine with windows computers via samba, you could turn off smbd and nmbd, are you not using a web server, turn off httpd. Not going to serve ftp to folks, turn of wu-ftpd or vsftpd(redhat default now) depending on which one is installed. It all really depends on what is installed. Post the list, someone can help you go through it.

h3r3tic:
In order for sendmail to listen for connections from other machines, you most likely need to change the configuration

find the file sendmail.mc (probably in /etc/mail at least that is where it is on redhat)
save a copy of it then edit the following line

DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

by removing the "Addr=127.0.0.1," from it.

save your changes, then, after backing up sendmail.cf run

m4 sendmail.mc > sendmail.cf

making sure of course that you are pointing to the correct file locations, those files are both in the same directory by default, so, no worries if you are running from that directory(on redhat anyway).

Then restart sendmail and it should accept connections from other machines, assuming that your firewall is not preventing it.

MAKE SURE THAT YOU READ UP ON HOW TO PREVENT SPAMMERS FROM USING YOUR MACHINE AS A RELAY BEFORE ENABLING THIS THOUGH.