If you're hard drive is formatted FAT32 then Vegas has to capture the footage in 4GB increments, because FAT32 doesn't allow files larger than 4GB. If you have an NTFS formatted drive, then you might have your caputre options set to limit the size of the clips, which could result in multiple clips.
I use NTFS drives but set Vegas to capture in 4GB increments, just so I can baciup the AVI files to DVD when I'm finished with a project.
You are apparently rendering to a drive that has been formatted as FAT32. On a FAT32 drive, no single file can be larger than 4 gig. 45 minutes of DV video would be around 9.75 gig, so I'm guessing you have two 4 gig files and a smaller third file.
If you are running Win98, then you have no choice but to let it split the files at the 4 gig limit. If you are running Win2k or WinXP, then you need to reformat your video drive as NTFS as NTFS does not have a filesize limit. (Well, it does, but it's around 12 terrabytes.)
If you just want to record it back to DV tape, then simply bring the three files onto the Vegas timeline, placed one after the other, and print it to tape.
Standard DV-AVI files are 13Gig per hour. So, 45 minutes would be just over 9 Gig which is exactly what you are seeing. If you want to render a more compressed version you can get it smaller. Since you are going to DVD, just render straight to MPEG2 at a bitrate that will be below 4Gig.
DV video is around 212 megabytes per minute. If you're looking to make a DVD then you render to MPEG2 AND you will need some DVD authoring software, like DVD Architect. I'm guessing you have never made a DVD before. My suggestion is to go to www.dvdrhelp.com and learn all about it.
Once you fix your drive issue you will be able to fit it on a DVD via DVD-A no problem. I made several 2 hour DVDs for my Dad last weekend, some based on MPEG2 rendered from NTSC DV AVI files that were approaching 20 gigs. However, I have not been able to fit more than 90 minutes on a DVD authored with DVD-A. I am sure it is possible but I will wait for winter to set in before sitting down to figure it out.
If you are rendering a Vegas project, you need to render using the Main Concept MPG2 codec and choose the DVD Architect video stream template. After rendering that file you render again, this time choosing the Dolby Digital AC-3 codec to render just the audio. Then use DVD Architect to author your DVD project and burn the DVD. Everything will fit perfectly on your DVD.
If you are using another DVD authoring program, RTFM and use Vegas to render out the correct MPG2 and audio format for that program. This might be an elemental MPG2 video stream and a PCM audio stream, etc. But if you're using Vegas and Architect just use the templates to pretty much automate the entire process.