"Is it possible to perform simple editing i.e.deleting part of a .flv flash video?"
FLV files create a kind of unique video editing challenge not readily solved by just opening the files in your favorite video editing application. The FLV format simply isn't supported by most video editing tools. You have two basic options for editing an FLV. Option 1: you can convert the FLV to another format and edit the converted file. Option 2: You can download an application specifically designed for FLV editing. In general I recommend going with editing software rather than conversion for a couple of reasons.
Converting FLV to Another Format
Converting FLV files to another format has one major advantage: you can convert FLV files with free software. If you plan on converting your FLV files to AVI or some other editing friendly format, the disadvantages often outweigh the advantages. Going from FLV to AVI or any other format often results in a file that looks worse than the FLV. Going from FLV to AVI also involves a bunch of extra time combined with increased artifacts in your finished file, because you're waiting to convert the file from FLV and then you're waiting again to convert back to FLV when you finish. Each conversion process introduces additional compression artifacts, which means your finished video will quite possibly look almost unwatchable compared to the original. If your budget is tight, MediaCoder and WinFF both do a great job of converting FLV to WMV, AVI or many other formats.
Editing FLV Files
Editing FLV files is a feature available in a much smaller set of applications. The one I currently recommend is FLV Editor Pro. It isn't as feature rich as using Adobe's Flash editing suite, but it's also affordable and gets the job done for basic editing functions. With FLV Editor Pro, you can trim sections out of your FLV, combine multiple FLV files, add watermarks over an FLV, insert special effects, and grab still images from an FLV, without needing to convert it to a new format. The time savings alone is probably worth the price, but the visual improvement over doing conversion is probably the real winner.