This is a big topic really, but here's my 2p ...
(I'll ignore the front-end apps and trading platforms which is a huge area with plenty of variables, but it should be noted that the selection of which software packages and solutions you choose will dictate the spec and quantity of your application servers. So I will only comment on the IT infracture excluding these app servers...)
This is the kind of back-end IT infrastructure a quality UK-based broker/dealer with about 10-20 staff would have:-
Servers: A pair of redundant HP Proliant DL380 servers running Windows Server 2008 or something equivalent. You might want to splash out on a backup solution like EMC Legato or Veritas NetBackup.
Messaging: Microsoft Exchange Server 2007. You could throw in a bunch of Blackberries for the big wigs too perhaps.
LAN infrastructure: Two or three stackable 24 port Cisco 3750 switches should do you nicely. Dual-monitor Dell PCs for everyone. Use them with Windows XP Pro, not Vista. Cat5e UTP cabling will need to be patched up everywhere for the phones and PCs - You will need a cabling contractor. PCs usually plug into the back of phones these days which helps.
WAN & comms: A 512k network service from BT Radianz (
BT Radianz: A Revolution in Connectivity) to connect to the financial world at large. A 2Mb ADSL/SDSL internet connection (
ISPreview UK - Independent Internet Service Provider Information Source) with static IP addressing for surfing, email, and hosting a website. Also chuck in an ISDN30 for the phone system - No firms use VoIP yet.
IT Security: Antivirus everywhere (try Symantec perhaps), and a pair of IP390 Nokia / Checkpoint firewalls to filter traffic in and out of the network. Do not use a Microsoft-based firewall. The FSA also likes to see IDS systems in use too, but they're effectively a waste of money IMHO.
Remote Access for home working: Cisco 3000 series VPN Concentrators are nice and easy to use with laptops. Lots of places use Citrix for remote access when there are no laptops, but it's quite pricey.
Phones: An Avaya IP phone system is good value and are dependable.
Redundancy / DR: If you're looking after other peoples' money, everything needs to be backed up and duplicated. This doubles the cost of everything, and makes it all three times more complicated to run. For offsite space and power for your hardware, check out
SunGard: Home Page.
Setting it all up: Hire an experienced network contractor for 2-3 months to set up the voice and data comms, and a Microsoft person for 3-6 months for all the email, home drives, AV, and general PC stuff. Get them to write comprehensive but simplified support docs so the receptionist can support it all once they're gone.
This is only one possible set of solutions from the top of my head, but it gives an idea of what a small-but-serious IT infrastructure could consist of. It could cost £40-100k or so ....