Eduardo,
You don't need any "special" hardware. Almost any hardware supported by redhat 7.3 should work. Stay away from ISA cards and WIN Modems. Go here to the FAQ, it has lots of good answers.
http://www.e-smith.org/faq.php3You might consider some larger hard drives. 40 gig less 5 for setup and swap leaves 35 gig left for use. This will only be 80 mb per user. if you add more users or some extra applications and the users start swapping large files then you may find yurself running out of space. I would use at least 80 gig as the are not much more $ than 40's ($96 verses $77 at my supplier)
Also consider two identical drives installed on each master ide channel. e-smith will automatically detect them and build a raid1 for you for redundancy.
By default, the setup only uses 3 partitions. /boot (100 MB), /swap (250 to 1000 MB depending on ram) and / (remainder of disk space). So by default the system allocates MOST of the disk space for use by whatever is needed. I don't know if you can bypass the default partition setup.
Fast processor and more memory will help speed things up during heavy periods. e-smith recommends the following:
# of Users-Up to 500
Usage-Heavy
Table 3.8. Hardware Requirements of a Category 4 Server
Architecture PCI-based Pentium-class processor
Processor speed 700 MHz (or better)
Minimum RAM 256 MB
Hard drive SCSI - at least 20 GB (2 large SCSI drives using RAID1 strongly recommended)
SCSI adapter Refer to SCSI Adapter section below (only necessary for SCSI systems).
Ethernet adapters Refer to Ethernet adapter section below.
Modem (for dialup only) Only modems that are Linux-compatible may be used. WinModems are not supported.
CD-ROM drive ATAPI or SCSI
Floppy drive any
Monitor any
Graphics card any
Mouse none required
Sound card none required
I would double the processor speed and ram as these are MINIMUM requirements.
If this will be an internal server then speed will matter greatly. If it is a server to the outside world then your actual speed will be determined by the internet connection, a slow machine will be less noticeable on a slower connection.