1. The less you write on an SSD the less you wear it. You can use the SSD for installing the OS which will improve the responsiveness of the OS and use the raptor you mention to store data that are not part of the OS like music, video, backups, etc...
2. Having an SSD and a HDD in a setup similar to the above mentioned won't impact the performance of the SSD
3. It is not a bad idea to hava a dual boot on your SSD as long as you know how to correctly set the offset and the alignment for the XP partition. A quick google search will help you on this. The Win 7 partition should be a lot bigger than the XP partition and I don't know if you will have enough space left for the rest of the applications you are going to install later on. It is wise not to completely fill the SSD with data but always leave an 8 - 10% free space.
I cannot tell you about XP and TRIM support as I have never combined those two.
4. The results vary according to the SSD you have and the clean erase you will perform.
I've done pretty much what you said except I don't understand the offset stuff. I did read an article and learned than the offset for my XP partition matches the the 32,256 byte default mentioned in the article. However, I don't know how to change it or what I should change it to. I used Partition Commander 11 to create the partition, making XP the first partition at 27GB. My Win7 partition is 47GB which leaves 6GB that I guess Intel sets aside to make the drive function properly. Both partions contain only the OS's and other applications, and each has about 18GB of free space. All docs, spreadsheets, pictures, music, etc. are stored on the Raptor.
If your system will support it, "XP Mode" is the ideal solution. Search the Microsoft site for XP Mode. It is a free download, and includes 32-bit XP Pro SP3. This will work in x32 or x64 Win7 professional, Ultimate, or Enterprise. You also need a processor that supports virtual mode, and a motherboard that supports VM, with VM turned on in the bios. I believe you can check your system compatability for XP mode at the MS site.
Benefits: no extra partition, no dual boot, no switching operating systems, runs whatever you want under XP, and the XP-run apps multitask and share space with everything you also want to run under Win7. XP Mode apps appear right in the Win7 Start Menu. And the result will take up very little space on your Win7 installation.
As for wear issues with your SSD, you probably do not need to worry. The drives are rated for mega terrabytes of write operations. However, you will lose the super fast performance of the SSD if you place data that is repeatedly acessed on a separate HDD, especially if the access involves small file-block sizes of 64KB and smaller. More of a concern might be space available for large amounts of data. Your solution of using a separate data HDD will work for that. You can also create a partition on an HDD that you link (use Disk Manager) to a folder on the SSD, making the process a bit more seamless.
You really don't need to worry about writing to this kind of SSD, unless you're putting it into a server that will write all day long. SSDs can write far more than most people are giving them credit for. As a desktop/laptop user, you should just use it as a hard drive, keeping in mind the alignment and trimming.
For the alignment, you need to use a tool that knows how to align partitions. Vista or Win7 install will. Personally, I would partition with Win7, then install XP, then Win7. You would have the 100MB partition Win7 creates, but it wouldn't hurt anything.