iMac 4,1 does not have Boot Camp update

What you have run into is a fairly common problem with any computer. Once they reach a certain age there stops being updates.

The problem is likely not just Apple. Consider that this Mac was released in 2006, going on thirteen years ago. I do PC/Windows support for a living and we have 5 year old computers with no driver updates available.

It is possible that if you find the make and model of the various components in your iMac (video, sound, network, bluetooth, WiFi, etc.) via Windows Device manager you may find some updates for drivers.

For example if you find that your iMac has a Broadcom L5105 (I made this number up for illustration purposes) chipset, then you would search for Windows 7 drivers for that particular chipset.

But I am betting that you are unlikely to find many (if any) driver updates for 13 year old hardware. Heck Windows 7 itself is end of life in just over a year and Microsoft won't provide any more updates to Windows itself after that.

According to the instructions Apple posted at the website Install Windows 7 on your Mac using Boot Camp, the Windows 7 installation media must include Service Pack 1 (SP1). If your media does not include SP1, then you should get a newer ISO file from the Microsoft website Download Windows 7 Disc Images (ISO Files). The download is free, but you will need to enter your Windows 7 product activation key to enable the download.

You can verify if SP1 has been included by selecting System from the Control Panel. Below is an example of what to look for.

Your iMac is a early 2006 model with 32 bit processors. So far you have not given a reason for needing a update for the Boot Camp drivers. The last released Boot Camp Support Software for your model Mac is on the Snow Leopard (OS X 10.6) installation DVD. Snow Leopard is still available for purchase from Apple. (See this website) Based on release dates, you might be able to use the Boot Camp Support Software on the Leopard (OS X 10.5) installation DVD.

Note: The Boot Camp Support Software will not appear on the Snow Leopard DVD if viewed from OS X (macOS). You must open the DVD on a machine running Windows. You will also probably need a DVD drive that can read dual layer DVDs (DVD+R DL).

Here is what is displayed when opening the Snow Leopard installation DVD on my Mac running High Sierra:

And, here is what is displayed when opening the same Snow Leopard installation DVD on my Mac running Windows 10:

Note The newer releases of the Boot Camp Support Software, which are available for download from Apple, are for the newer Macs. These releases are not updates that can be used on older Macs.

Normally, any updates to the Boot Camp Support Software are provided by Apple by running Apple Software Update while booted to Windows. I believe the Apple Software Update provided with the older Boot Camp Support Software no long works. You can get a newer version of Apple Software Update by installing Apple products such as iTunes, but these versions of Apple Software Update with not provide updates to the Boot Camp Support Software for your older model Mac.

Often Microsoft will provide updates for drivers for older Macs. With Window 10 this is done automatically once Windows is installed. Also, the Windows 10 iso will already contain most of the drivers needed to run the operating system.

Once windows is installed, you can open the Device Manager to see if there are any driver problems. Just because the Device Manager shows a problem does not mean there is actually a problem. Many Macs contain redundant or unneeded hardware. When the Boot Camp Support Software is run after you finish installing Windows, Null drivers are installed that pacify this hardware. This also causes the Device Manager to not show errors for this redundant or unneeded hardware. Often, when you install a version of Windows that is not officially supported by Apple for your Mac, the Device Manager will show errors. If your Mac appears to be functioning normally, then you can ignore these errors.

FYI: It is possible you could run 32 bit Windows 10 on your model Mac by using the drivers on the Snow Leopard DVD. Windows is designed to use older drivers when newer ones are not available.

I also should mention that to run Windows you should make sure you have the latest firmware installed. For your model Mac, you have to manually install these updates. The latest update for your Mac can be found at the Apple Website: About EFI and SMC firmware updates for Intel-based Mac computers.