I run a linksys wireless router. I've found no settings that would prevent me from connecting my computers. The computers are able to connect sometimes, it's just not predictible.

I'm using the sync function built into Vista

I've checked my IP's, Subnet masks, and gateways, all are in the same "local area" if you will.

The built in Vista sync isn't designed to sync to computers. Excerpt below from Microsoft's Windows Vista sync info page:

Computer-to-computer sync Windows Vista offers several ways to keep information synchronized between your computer and your devices. The one thing it can't do, however, is sync files and folders between computers.
Fortunately, Microsoft has created a program called SyncToy to fill the gap. SyncToy makes it easy to keep files and folders synchronized between one or more computers. Best of all: you can download SyncToy for free from the Microsoft website.

Microsoft Link for the above:
Windows Vista Help: Solving the mystery: How to keep your devices in sync

You need to use synctoy which is free from Microsoft: See link below:

Download details: SyncToy v1.4

Try using synctoy as if you still have problems please post back.

I've downloaded synctoy. This is a tool like what I have been looking for, but I still have the same issue of being able to connect to my desktop from my laptop.

I think this issue trancends the synctoy or any sync function. It is a problem of not being able to access my desktop from my laptop. They are both on the same local network but they only seem to be able to talk when both are booted up at the same time. If my desktop has been on for awhile and I boot up the laptop, the laptop isn't able to connect to the desktop. Funny thing is, I can access the laptop from the desktop.

Perhaps part of the issue has to do with offline files. The way I had the sync set up before synctoy was making files on my desktop available offline on my laptop (accomplished by accessing the desktop files from laptop, right clicking, and selecting "make available offline". Maybe this has created a problem for the laptop?

Thoughts?

Technically it should still connect and synchronise the files - with synctoy its an on demand thing. How are the IP's configured. You should really set them manually not by DHCP to avoid these sorts of problems. To check the XP pc - Click Start > Run > type: cmd > Click OK
At the prompt type: ipconfig /all > press enter. If is has DHCP Enabled: YES, then this could be part of your problem. Try setting the IP address manually.

I would also use mapped network drives. It makes things much easier. On the PC map the shared folder on the XP and then set it to make available offline and to synchronize on log on and log off. You can also synchronize anytime you want.

To map a network drive, on the vista do the following:
1. Click Start > Computer
2. Click Map Network Drive
3. In the windows that opens in the folder section type the following: \\192.168.1.2\XPDocs
Replace the 192.168.1.2 with XP PC's IP Address and the XPDocs with the name that you chose when you shared the folder.
4. Make sure there is a tick in Reconnect at Logon. Click Connect Using a different user name. Type in the username and password that you setup earlier on the XP PC. Click OK.
5. Click Finish

Please post back if you have any problems or if this doesn't fix your problems.