To convert a Windows PC to a virtual machine, the task is much easier and more straight-forward with VMWare VCenter Converter. However, if you want to follow a path similar to this tutorial for Windows, it should be viable. In addition to Clonezilla, Windows7 also comes with a system image creating utility in its Backup and Restore center (check here).
VCenter Converter is also an alternative to the current approach. However, VCenter Converter can only be installed on a Windows machine and the conversion of a Linux system should be done as converting a remote source. In other words, one runs the Converter in Windows and specify the IP address of the Linux system that is to be converted. I tried this method before, but the problem for me was that the Converter cannot gain root access to the remote Ubuntu system via my username, which was already an administrator. I found a plausible solution in VMWare's knowledge base (1008164), but I didn't succeed by following it.
Note, there are other alternatives to Clonezilla, for example, Partimage and FSArchiver. If you use Partimage, be careful since it does not support imaging of an ext4 file system (ref), which is popular for Linux OS nowadays and your Linux system is very likely to be on. However, FSArchiver does not have this problem (ref).
[:(] Turned out I didn't actually succeed in Step 3 when carrying my Ubuntu from a dual-boot physical machine to a virtual machine. For the dual-boot machine, I only used Clonezilla to image the Ubuntu related partitions. When carrying this image onto the virtual disk, Clonezilla still did well. However, the virtual machine wouldn't boot from this virtual disk. I checked why and found that, although content-wise Clonezilla only imaged those of the Ubuntu partitions, when it came to disk layout, all partitions were covered. As a result, when restoring from the image to the virtual disk, Clonezilla created partitions proportionally (if not exactly) the same to the physical disk, resulting in both Ubuntu partitions and non-Ubuntu partitions (this was also why the size of the virtual disk needed to be no smaller than the physical disk). Then, the Ubuntu partitions were restored with the backup content, leaving the non-Ubuntu partitions empty. As a result, probably, the Master Boot Record (MBR) was not correctly installed/restored onto the virtual disk (remember that the virtual disk was a fresh disk without any existing boot mechanism), leaving it an unbootable hard drive. [:)] I resorted to FSArchiver eventually and succeeded. What I did was: 1) Similar to Step 1 but using FSArchiver, 2) Similar to Step 2 but creating a loaded virtual machine with Ubuntu installed, and the virtual disk was only larger than the imaged partitions, 3) Overwrote the Ubuntu partitions in the virtual machine with the imaged partitions. As a result, since the MBR was already there before restoring from the image backup, the virtual machine booted correctly from the virtual disk. I happily saw my old Ubuntu in VMWare Player. But be aware, there was still a little problem related to the swap partition. At booting, the restored Ubuntu warned me of error finding the swap partition every time, since I didn't image and restore the swap partition from the physical machine. Comments and suggestions to clarify this issue and provide fixations are welcome via email.