Hmm, seems to be a BULL copy of an IBM power 5+ machine.
I can only assume the "ESCALA PL250T+ SYSTEM" includes a basic configuration of enough to make a running system and then they have specified some extra hardware. Otherwise they have specified a raid card for only one hard drive!!
No mention of an operating system or licence for the same!
Do you need a DVD writer, a 36GB 4m tape drive and an external 2.5g tape? - you could buy a CD or DVD ROM and backup to a tape drive.
Do you need the graphics card? Does your existing system have a graphics card?
If you need the graphics card, or not, I see no mention of the USB keyboard, mouse and monitor you will need to use it.
Do you need the extra serial ports - "16 port Digi Port Server II, RJ45", IBM do a dual port card if you need more than just console or modem access - the system will have a couple of serial ports but they are not full RS232 ports so you need a rs232 card if you need to use more than a dumb console or console access over a modem.
If you are not using it in an office environment you won't need the sound kit - OEM DESKSIDE COVER SET.
I'd ask an IBM bp / var / reseller for a similar spec (new and used) p505 / p510 / p511 / p520 and see how it adds up.
Without knowing anything about your current hardware it is impossible to say how this might compare to what you already have.
If your existing kit is over 10 years old and you don't have any performance problems with 75 users, you can probably get what you need for 500 users second hand from a reseller for about 5k to 10k and it will run AIX 5.3 and IBM will support it for many years to come.
If your 10 year old box was a top of the range at the time the spec you mention might be no better (or much worse) than what you have!
There is a p520 on ebay UK at the moment (similar spec without the added bits) with a starting bid of £2600, keep an eye on it for an idea of what they are going for;
http://cgi.ebay.co.uk/9111-520-IBM-p...QQcmdZViewItem
If you have the space (and huge amounts of power ;-) there is also a p680 currently at just under 1.2k and that will run rungs around a tiny p5 box like the Bull:
http://cgi.ebay.co.uk/7017-S85-IBM-p...QQcmdZViewItem
As I say, with no idea of what you have there is no way to tell if this system is any better or worse than what you currently have.