I don't know if your distro (slackware I presume) has configured auto mounting. There are several options, depending on whether you want to use automounting and have it mounted on /media, or if you would rather mount it manually.
If you use the KDE 4 desktop, there is a "Device Notifier" widget you could add to your panel. This is assuming that the other components are set up for automounting. It may be all you are missing.
Also look at the "ivman" package. Mounting an external drive could be as simple as "halmount /dev/sde2" for example.
You could create an entry for your firewire drive in the /etc/fstab file. Use the "blkid" program as root to identify the UUID number of the drive. Here is an example:
sudo /sbin/blkid /dev/sde2
/dev/sde2: UUID="5783d30e-8dc4-447a-80f4-8952129e9d9e" TYPE="ext3"
You can also look at "ls -l /dev/disk/by-uuid/*" to identify the UUID. Some people prefer to use the label of the filesystem instead.
Now in my example, I could add:
UUID=5783d30e-8dc4-447a-80f4-8952129e9d9e /mnt/firedrive ext3 rw,user,noauto,user_xattr,acl 0 0
to my /etc/fstab file. This would allow me to mount this ext3 filesystem as a normal user. The options will vary depending on the filesystem you are using. In particular (user_xattr,acl) won't be used for a VFAT or NTFS filesystem.
is used to prevent a bootup failure if the drive isn't plugged in when you boot.
option is used to allow a regular user to mount this filesystem. (for vfat or ntfs you also need uid=<yourusername>)
If you have something else in mind or have further questions, please provide more information. Your disto you are using, your desktop environment, the filesystem used on the external drive and where you want to mount it.