I find XP based systems will lag after they been in use for yrs. Users, report just as you. The only cure, if you want to call it that is to reload the OS and restart all over again. The main reason the results are like this is because all the XP updates, etc.. will strangle the system over time to include any past installs, etc.. You may want to try some registry cleaner, etc., but that's up to you. Point blank, there is no easy fix other than what I offered in the beginning, start afresh. Of course, back-up critical data, etc. beforehand. If you have access to a new HD or cleaned HD, you swap data over or clonezilla it. Doing so will remove any noncontinuous data segments, etc..
Ok, here is a weird one. When I boot my machine in the morning, it takes 6 to 7 minutes to boot. The box goes through the POST and then hangs, nothing on the display, the only indication I get that the box is even working is the disk drive light remains active and flickers occassionally. Now here is the twist, once the box boots for the first time in the morning it boots normally all day after a power down usually under 1 minute. I have ruled out anything to do with XP since it reboots fine. I have swapped out the RAM, the power supply, the video card, reset the CMOS, and replaced the battery, No Joy. I can't figure out what would be effected by an extended period of no power. My next step is to replace the drive, its the only thing left that I haven't swapped out. Has anyone else had this issue or know what the root cause is. Thanks in advance.