there are a good number of services you can either shutdown and disable permanently or shutdown and set to manual start...i'd start with the aero graphics, the widget manager, task scheduler, superfetch and windows update, then work your way through the list...there are several very good resources that can tell you what services are safe to shutdown in vista, some even have descriptions of what each service does...you should be able to get below 50 processes on a fresh boot fairly easily.
i had to hack the registry to get rid of some program autostart files, like punkbuster, acrotray, acrobat reader quickstart, etc...after a reboot and shutting down my anti-virus i have around 35 processes running before opening ah...tried to get it under 30 but,

it got ugly.
http://www.howtogeek.com/howto/windows-vista/disable-aero-on-windows-vista/http://www.howtogeek.com/howto/windows-vista/how-to-disable-superfetch-on-windows-vista/this is the list i started with, part of skuzzy's recommendations:
Base Filtering Engine
Certificate Propagation
Distributed Link Tracking Client
Fax
Internet Connection Sharing (only safe if you are not sharing your Internet connection on your local computer)
IP Helper
Messenger Sharing Folders USN Journal Reader Service
Net.tcp Port Sharing Service
Offline Files
Parental Controls
Remote Registry
Routing and Remote Access
Server
SSDP Discovery
Telephony
Tablet PC Input Service
Themes (this is a huge resource hog)
UpnP Device Host
Windows Error Reporting Service
Windows Media Center Extender Service
Windows Media Center Receiver Service
Windows Media Center Scheduler Service
Windows Media Center Service Launcher
Windows Remote Management
WinHTTP Web Proxy Auto-Discovery Service
Windows Media Player Network Sharing Service (this is a nasty one. It causes all manner of pauses and stutters and will spontaneously reappear even when it is stopped)
optional:
Windows Defender (also be sure to disable it from starting in the Start->Run->msconfig startup tab)
this stuff can be set to "manual start"...that way they are still available to the system when needed:
Application Experience
Application Information
Application Layer Gateway Service
Application Management
Block Level Backup Engine Service
CNG Key Isolation
COM+ System Application
DFS Replication
Diagnostic Service Host
Diagnostic System Host
Distributed Transaction Coordinator
Extensible Authentication Protocol
Function Discovery Provider Host
IPSec Policy Agent
Link-Layer Topology Discovery Mapper
Microsoft .NET Framework NGEN V2.0.50727_X86
Microsoft iSCSI Initiator Service
Microsoft Software Shadow Copy Provider
Peer Name Resolution Protocol
Peer Networking Grouping
Peer Networking Identity Manager
Performance Logs and Alerts
PnP-X IP Bus Enumerator
PNRP Machine Name Publication Service
Portable Device Enumerator Service
Problem Reports and Solutions Control Panel Support
Protected Storage
Quality Windows Audio Video Experience
Remote Access Auto-Connection Manager
Remote Access Connection Manager
Remote Procedure Call (RPC) Locator
SL UI Notification Service
Smart Card
Smart Card Removal Policy
SNMP Trap
Terminal Services Configuration
Terminal Services UserMode Port Redirector
Thread Ordering Server
TPM Base Services
Virtual Disk
Volume Shadow Copy
Windows Backup
Windows Cardspace
Windows Color System
Windows Connect Now – Config Registrar
Windows Driver Foundation – User-mode Driver Framework
Windows Event Collector
Windows Image Acquisition (WIA)
Windows Module Installer
Windows Presentation Foundation Font Cache 3.0.0.0
Wired AutoConfig
WLAN AutoConfig