My SR2 matrix knowledge is sketchy at best, but a look at the system shows that it's fairly weak except for the inital access point and the core/file stores. They also seem to favor black and grey IC. I'd do it as a two tier system using their previous iconography. The "castle" is the second host in the list. Every terminal in the office would give access to the corporate host, but the only direct connection into the secure host would be from the executive computers. Other users would need to sleaze their way past the dragon to access the secure host.

Depending on how good your decker is, you may want to tone this down a good bit. The first host is on the high end of easy and the second is on the bottom end of average.

System: Sylvan Information Corporate Host
Ratings: Orange-6/10/9/8/10/10
Security Sheaf:
4 Scout-5
8 Tar Pit-7
11 Passive Alert, Crippler (Masking)-5
16 Crippler (Body)-7
19 Probe-7 with trap Sparky-7
22 Tar Pit-7
25 Active Alert, Killer-7
29 Psychotropic (Judas)-5
34 Lethal Black IC-9
39 Killer-5
43 Non-lethal Black IC-9
47 Lethal Black IC-7
52 Shutdown
Iconography: The entire system appears as a primeval forest. The sculpting is beautiful, and there is no sign of UMS iconography in the host. Most data traffic here is represented by streams with fish swimming inside.
Access: The access subsystem is generally sculpted as a series of bridges and drawbridges guarding the icons of whatever the decker wishes to manipulate. Crossing one of these "bridges" is the equivalent of defeating the access subsystem.
Control: These icons appear as a wide variety of items mostly with a strong theme of nature. Some examples include natural "scrying" pools, large stones of apparent occult significance, and crystal balls set on stands.
Index: The index subsystem is represented as a series of forest signs and trail markers. These range from large white arrows on posts to scrapped runes on standing stones.
Files: Each file is represented as a tree or rock. The leaves spell out the individual pieces of the files when read.
Slaves: Each slave system is represented as a small tower or cottage. These slaves are generally controlled with an archanic set of levers located inside the cottage/tower and are guarded by a knight or peasant. Getting past the peasant is the equivalent of defeating the slave subsystem.
IC Iconography: Combat IC in this host is sculpted to appear in the forms of wild animals of roaming knights. Trace IC is usually a hunting dog, while probe and scout IC generally appears as a bird or other "natural spy".

System: Sylvan Information Secure Host (Sensitive Data only)
Ratings: Red-7/12/10/12/12*/10
Security Sheaf:
3 Construct-5(Probe-7, Killer-3) w/Expert Defense
7 Tar Baby-7
10 Scout-7
13 Crippler (Masking)-9
15 Scout-5 with Trap Sparky-9
19 Passive Alert, Scout-7 with Trap Killer-7
23 Tar Pit-5
26 Blaster-7
28 Blaster-9
32 Trace-5 with Trap Blaster-5
35 Active Alert, Ripper (Evasion)-5
38 Cripper (Bod)-5
41 Lethal Black IC-7
44 Non-lethal Black-5
49 Scout-7
52 Shutdown
Iconography: This system is a castle in the forest of the main corporate host. Getting inside requires evading a large black dragon, a drawbridge, and a line of elven knights (ie, the access subsystem).
Access: Aside from the overly elaborate entry SAN, the access controls inside the host are invariably large oaken doors, locked and carved with arcane runes.
Control: Most control subsystems inside the castle are represented by large wooden or steel levers. Pulling these levers grants access to a subsystem and the way in which the levers are pulled performs the actions. Most of these levers, when pulled incorrectly, can trigger traps.
Index: In the central room of the castle, a large stone is inscribed with mystic runes. These runes are the index system of the castle. A sword icon is inserted into the top of the index stone, with no apparent purpose.
Files: Files inside the castle are represented as lines and lines of books inside small libraries. Some of the books are cursed, however (tapeworm IC-7, or databomb IC-5).
Slaves: The castle itself does not control many slaves. Those that it does control are the spires of the castle's towers. Climbing inside the tower past the guarding knights (subsystem) allows for control of the system. I/O is usually handled through small reflecting pools of mystical glowing water.
IC Iconography: Combat IC in this host is sculpted to appear in the forms roaming knights or traps. Trace IC is often a servant who trails the intruder, while probe and scout IC generally appears alert guardsmen.