The cidaemon.exe is not tied to your Anti-Virus program, those should be defwatch.exe, vptray and one other thing, I believe for NAV. The cidaemon.exe file is associated with the indexing services on Windows XP. This service is not required for the stable operation of Windows XP and can be disabled by accessing the services and disabling the Indexing service. This will free up sometimes up to 2MB of memory and of course it frees up the CPU.
Here are some other services you can set to "Disabled" if they are currently being loaded to help in saving memory. Please research these services and how they apply to your system before disabling them. What may work for one system may not work for another, though I have disabled all of these services and have not run in to any issues. Ones with (network) next to them may be required if on one.
Alerter
Automatic Updates
Background Intelligent Transfer Service
ClipBook
Computer Browser (network)
Distributed Link Tracking Client (network)
Error Reporting Service
IPSec Services (network or VPN)
Messenger
Net Logon (This IS required if you have a network/domain you log on to)
NetMeeting Remote Desktop Sharing
Performance Logs and Alerts
Portable Media Serial Number
QoS RSVP
Remote Desktop Help Session Manager
Remote Registy Service (XP Pro only, network)
Routing and Remote Access (XP Pro only)
Secondary Logon (network)
Server (required if you are sharing any resources off of your computer)
Smart Card
Smart Card Helper
TCP/IP NetBIOS Helper (network)
Upload Manager
WebClient
Wireless Zero Configuration
WMI Performance Adapter (network)
Windows XP also uses Prefetch that preloads programs at boot and programs that you often use, you can disable this by altering this registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters\EnablePrefetcher
Set the value to 0
There tons of tweaks out there, for XP try www.tweakxp.com.