There's no upgrade from XP to Win 7. You'll have to wipe the hard drive and do a clean install. So any drivers that are installed now will be lost. And all your personal files will be lost too so you have to back them up up on external media first, and be sure to have your software product keys and installation media for any software (eg, MS Office) because you'll have to reinstall everything

Dell doesn't support Win 7 on the Dimension 8300. So you should run the free Windows 7 Upgrade Advisor to see if your system is capable of handling Win 7 and what drivers and software may be a problem. You can watch the video here for advice from Microsoft on going from XP to Win 7.

And to answer your specific question, that driver may be installed when you install the chipset after loading Win 7, or it might be the driver for a Conexant (dial-up) modem. So if you're using an Ethernet port to connect to the internet, you may not even need to install drivers for the modem.

Most of the drivers for this system will be installed natively with Windows 7. Although this system should run Windows 7 32 Bit, its not a very economic upgrade and this system has weak hardware so it will be on the edge of system requirements.

Windows 7 has reached end of retail sales so its harder to get a retail Windows 7 license. It is much more economical to buy a second hand business model such as an OptiPlex 760/780 that come with a Windows 7 OEM license. The OEM license and the second PC will be cheaper than the retail Windows 7 license and the second hand PC will significantly outperform he Dimension 8300.

You can also look at buying a new Inspiron Desktop which will come with Windows 8.1 64 Bit.

Windows 7 will reach end of mainstream support in 2015. Extended Support is available until April 2020 however so it will continued to be patched. The Windows 7 userbase is very strong and very important to Microsoft in industry. Most of industry will skip the Windows 8 family entirely and migrate to Windows 10 eventually.

http://windows.microsoft.com/en-us/windows/lifecycle

• Mainstream support—Microsoft will offer mainstream support for a minimum of 5 years from the date of a product's general availability, or for 2 years after the successor product is released, whichever is longer. For example, if you buy a new version of Windows and five years later another version is released, you will still have two years of support left for the previous version.

• Extended support—Microsoft will offer extended support for either a minimum of 5 years from the date of a product's general availability, or for 2 years after the second successor product (two versions later) is released, whichever is longer.

As mentioned Windows 7 has reached end of mainstream support and hence retail/OEM sales. Even if you can buy a new Windows 7 license, the cost is likely to be more than a second hand OptiPlex 760/780 with a Windows 7 OEM license. Windows 8.1 is unlikely to run well on your computer.

If you are going to go to Mac and hence have no Windows dependency on software you may try to install the 32 Bit version of Linux Mint, Ubuntu or Fedora which you can install for free. The Mac OS is basically a commercial Linux OS.