Here's the situation:

I've got a Debian Lenny server with no GUI. I need to have a windows XP virtual machine that is accessible to all the clients on my network. I've accomplished that with virtualbox. However...

I MUST have usb support. It would be preferable to have it across the network, but it will suffice if I can plug my usb devices into the server. However, my attempts to create a usb filter on a headless server with virtualbox have all met with failure, and nobody on the entirety of the internet seems to know how to address this problem. I've tried everything I can think of. So...

What software can I use that gives me usb support on a headless machine and does not require fancy hardware (like kvm does)?

xen have a look at their site: http://www.xen.org/

VMWare workstation works fine with USB. I don't know about VMWare player, but I would expect it to also work.

Workstation ain't free, but it is very good.

Vmware workstation is a bit beyond my budget. As for xen, doesn't it require a special kernel? I've been looking at their website a bit and it does look like an interesting bit of software,

I'm not adverse to sticking with virtualbox if I can get the thing to work. Let me ask this: is there anyone here who has gotten usb devices to work on virtualbox headless?

My main web server that I use is a Xen VPS/VDS (I own the hardware too but making the main hosted stuff a VM just makes it so much more portable), it works very well but it works well, I had my VPS up at the longest point about 450 days... then the slave bar it drew power from in the datacenter tripped so the VPS would have gone longer if not for that. Also Xen is owned by Citrix so it's got a fairly good/big name behind it.

I have used VMware before but you have to watch the licensing on it, generally non-commercial licenses (no reselling of VMs in other words) are free, while commercial (reseller licenses) cost dearly, you do have to be very careful and really read the license agreements. Also certain versions only have commercial licenses. VMWare player on windows allows for connecting USB, I am not sure about Linux.

There is also KVM(Kernal-Based Virtual Machines) to think about, it seems to be gaining some popularity around, I hear of it more then I did a year ago so it might be an upcoming thing.

There's two versions of VirtualBox: the open source version (OSE suffix), and the PUEL version. Only the PUEL offers USB support.

http://www.virtualbox.org/wiki/Downloads

With Xen you can have USB support on guests, for this you must trick the domU configuration file and filter the device you wish to share with your virtual machines.
For what I understand, you have no GUI at your server so you must run Xen with VNC and access the console from the network in other computer. An good option is install libvirt on the server or some other utility to view your running VM's.
VMWare have free options and work very well on linux, I used to use VMware and the Server license is free for Non-Commercial use. You should download and install on your system from source or packaged.

For more information you can try Virtuatopia and Xen for Debian Wiki. Just google that.

I hope you can choose your better option.

You might get better answers about achieving what you want using VirtualBox by asking at http://forums.virtualbox.org

http://pve.proxmox.com Very easy to setup and get working , very good support. Has a web based UI and uses KVM (Kernel Virtual Machine) and OpenVZ) and now just recently KSM has been implemented because of the new release of qemu which really helps out memory usage when using the same type of OS or virtual machine. Check it out.