Not natively. Windows (and for that matter other PC operating systems such as Linux) can’t execute Macintosh programs and PCs cannot boot any flavor of the MacOS; similarly, the MacOS can’t launch Windows applications and a Macintosh computer will not boot Windows or any other PC operating system.
You can do at least some of this in emulation though. Emulation is where you run a program, and the program duplicates the functions of the logic boards and chips of the other hardware platform and then converts all that stuff to signals that make sense to the real (and different) logic boards and chips that the computer actually has. Inside the emulation program, operating systems that can’t boot natively can boot up, and once they do, programs written for that operating system can run.
Emulated computers are slower than real computers. An instruction is processed a lot faster on a real logic chip that has actual circuits than it is by an emulation program that takes those instructions and reproduces the functions of those circuits.
The Macintosh can run a very sophisticated commercial emulator program called VirtualPC, which is now owned and sold by Microsoft. There are versions of VirtualPC that will run under MacOS 9 and versions that will run under MacOS X. Within the emulated PC (a make-believe Pentium box with a Sonnet S3 Trio video card, SoundBlaster compatible sound board, standard 101 key keyboard, etc etc), VirtualPC will allow you to install pretty much any standard PC operating system you want, from DOS 3.0 to XP Professional, Red Hat Linux to OS/2. Then, once the OS is installed, you can install PC programs appropriate to that OS and run them there. VPC will let you network and go online and access peripheral devices such as USB scanners and printers. It won’t necessarily work with peripherals that have connectors that the Mac does not have (parallel ports, PC serial ports, PS-2 mouse ports), though, even if you use an adapter, and probably only limited use of PCI cards (e.g., the card that gives you a second monitor under MacOS will not be seen by the PC environment because the emulated PC environment consists of a single Sonnet video card). An actual PC hard drive plugged into the Mac cannot be accessed by the emulated PC unless the Mac can also see and mount it (which pretty effectively eliminates access to NTFS-formatted drives, although FAT32 drives work OK) and even if you can see it you can’t boot your imitation PC from it — VirtualPC boots from a hard disk image file only.
On the flip side of things, the PC world has no equivalently solid Macintosh emulator but does have a collection of mostly free Mac emulators that each provide some functionality. The most robust of these are Basilisk II and SheepShaver, which run under PC Unix operating systems and under most flavors of Windows. Basilisk II emulates a Macintosh from the pre-PowerPC era. I don’t know the details of what it emulates in terms of other hardware, but the CPU instructions it knows how to deal with are those of the Motorola 68020, 68030, and 68040 (“68K”) chips. Basilisk II requires the presence of a Mac ROM file which needs to be obtained from an old relic Mac from the Macintosh IIx era through the Quadra era. Once you’ve got that, you can install Macintosh System 7 or early MacOS 8 from Mac installation diskimages, or you can download (legally, freely) bootable diskimages of System 7 and then insert a later Macintosh installation CD and upgrade to a later version. Under Windows, Basilisk does networking including AppleTalk and TCP/IP and it can go online. SheepShaver emulates a PowerPC chip and while it will not let you boot MacOS X it will let you install PowerPC versions of the Classic MacOS such as MacOS 8.6, and run PowerPC versions of Mac software. I should point out that doing so does not make it faster than Basilisk II — a real PowerPC Mac is faster than an old Quadra but if you have to emulate them both on the same PC emulating the Quadra is faster. But lots of software is not available in even moderately up-to-date versions that will run in the 68K Mac environment. Then there is PearPC, a new emulator, which will let you install MacOS X and run the latest Macintosh software — very slowly for now, because it is very new. They do appear to have networking functioning in both the Windows and the Unix builds of PearPC, though. (PearPC will also allow you to run PowerPC operating systems other than MacOS, such as Mandrake Linux for PPC). As with VirtualPC, Basilisk and Sheepshaver and PearPC will not let you boot from an actual Mac hard disk (they all boot from diskimages). In some builds you can boot from a Macintosh high-density floppy though.